Carbon material, method for producing carbon material, and non-aqueous secondary battery using carbon material

ABSTRACT

A carbon material for a non-aqueous secondary battery containing a graphite capable of occluding and releasing lithium ions, and having a cumulative pore volume at pore diameters in a range of 0.01 μm to 1 μm of 0.08 mL/g or more, a roundness, as determined by flow-type particle image analysis, of 0.88 or greater, and a pore diameter to particle diameter ratio (PD/d50 (%)) of 1.8 or less, the ratio being given by equation (1A): PD/d50 (%)=mode pore diameter (PD) in a pore diameter range of 0.01 μm to 1 μm in a pore distribution determined by mercury intrusion/volume-based average particle diameter (d50)×100 is provided.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of International Application PCT/JP2015/069574,filed on Jul. 7, 2015, and designated the U.S., (and claims priorityfrom Japanese Patent Application 2014-139782 which was filed on Jul. 7,2014, Japanese Patent Application 2014-234606 which was filed on Nov.19, 2014, Japanese Patent Application 2014-248251 which was filed onDec. 8, 2014, Japanese Patent Application 2015-064897 which was filed onMar. 26, 2015, Japanese Patent Application 2015-067180 which was filedon Mar. 27, 2015, Japanese Patent Application 2015-067184 which wasfiled on Mar. 27, 2015, Japanese Patent Application 2015-067194 whichwas filed on Mar. 27, 2015, Japanese Patent Application 2015-067201which was filed on Mar. 27, 2015, Japanese Patent Application2015-122197 which was filed on Jun. 17, 2015 and Japanese PatentApplication 2015-122198 which was filed on Jun. 17, 2015,) the entirecontents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a carbon material, a method forproducing a carbon material, and a non-aqueous secondary batteryincluding a carbon material.

BACKGROUND ART

In recent years there has been an increasing demand forhigher-performance non-aqueous secondary batteries having high energydensities and excellent high-current charge-discharge characteristics,and there has been a need to achieve further increases in capacity,input and output, and service life.

It is known that in non-aqueous secondary batteries, carbon-basedmaterials, such as graphite, are used as carbon materials that serve asnegative electrode materials (negative electrode active materials).Graphite, which has a high degree of graphitization, can provide acapacity near 372 mAh/g, which is a theoretical capacity of lithiumocclusion, and is low cost and durable, and thus is suitable as a carbonmaterial for non-aqueous secondary batteries, particularly, lithium ionsecondary batteries.

Patent Document 1 has disclosed a technique for improving fillingproperties and fast charge-discharge characteristics by treating a flakenatural graphite with mechanical energy to prepare a spheroidizednatural graphite and coating the surface of the spheroidized naturalgraphite, a core graphite, with amorphous carbon.

Patent Document 2 has disclosed a technique for reducing the expansionduring charging and discharging by spheroidizing a spheroidal graphiteto inhibit the crystal orientation of graphite particles. PatentDocument 3 has disclosed a technique for improving fast charge-dischargecharacteristics and cycle characteristics by isotropically pressurizinga spheroidized graphite obtained by spheroidizing a flake graphite toproduce a highly isotropic graphite having a high density with nointra-particle voids.

Patent Document 4 has disclosed a method for producing a powdered carbonmaterial by mixing a flake natural graphite, a meltable organicsubstance, and a pitch having a softening point of 70° C. under heating,applying a mechanical impact with a hybridizer, adding carbon black,applying another mechanical impact to prepare a spheroidized powder, andburning the powder. Patent Document 5 has disclosed a method forproducing a spheroidized graphite particle having a smooth surface byadding a resin binder to raw carbon material (raw graphite) particlesand spheroidizing the mixture. Patent Document 6 has disclosed a methodof rapidly stirring coal-derived calcined coke and paraffin wax underheating to produce spheroidal particles.

Patent Document 7 has disclosed a carbon material produced by burning aspheroidized natural graphite in an air atmosphere at 650° C. using amuffle furnace and removing fine powder on the particle surface.

Patent Document 8 has disclosed a carbon material having an increasedamount of micropore produced by irradiating a spheroidized naturalgraphite with ultrasonic waves in a circulating ultrasonic homogenizer.

Patent Document 2 has disclosed a carbon material having a frequency ofparticles with a diameter of 5 μm or less, as measured after ultrasonicwaves have been applied for 10 minutes, of 40% to 85%.

Patent Document 9 has disclosed a technique for improving fillingproperties and input-output characteristics by treating a flake naturalgraphite with mechanical energy to prepare a spheroidized naturalgraphite and coating the surface of the spheroidized natural graphite, acore graphite, with amorphous carbon.

Patent Document 10 has disclosed a technique for improving input-outputcharacteristics at low temperatures by loading carbon black particlesand amorphous carbon onto the surface of a spheroidized graphiteobtained by spheroidizing a flake graphite to form a fine structure onthe particle surface.

Patent Document 11 has disclosed a multi-layered carbon materialcomprising a carbide of an organic substance deposited on the surface ofa graphitic carbonaceous material; by controlling the residual amount ofthe carbide of an organic substance to be 12 parts by mass to 0.1 partby mass based on 100 parts by mass of the graphitic carbonaceousmaterial, a non-aqueous solvent secondary battery can be produced havinga high discharge capacity, a low charge-discharge irreversible capacityin an initial cycle, and a high level of safety against electrolytesolution.

Patent Document 12 has disclosed a composite carbon material made ofhigh-crystallinity carbonaceous particles and a low-crystallinity carbonmaterial on the particle surface; by controlling a tap density to be0.43 to 0.69 g/cm³ and the percentage of carbon materials having amicroscopic Raman R value of 0.2 or larger to be at least 20%, anon-aqueous solvent secondary battery having excellent low-temperaturecharacteristics can be produced.

Patent Document 10 has disclosed composite particles of graphiteparticles and carbon fine particles having a primary particle diameterof 3 nm to 500 nm; by controlling an R_((90/10)) value, a ratio of amicroscopic Raman R value at 90% from the smallest value to an R valueat 10%, to be 1 to 4.3, a non-aqueous solvent secondary battery havingexcellent input-output characteristics at low temperatures can beproduced.

Patent Document 14 has disclosed a technique for controlling a porevolume by selecting conditions of curing and carbonizing a phenolicresin or other resins. Patent Document 15 has disclosed a technique forcontrolling a tap density, a specific surface area, and a pore volume bycoating agglomerated particles obtained by isotropically pressurizingflake graphite particles and spheroidized graphite particles each withlow-crystallinity carbon and blending the coated particles.

Patent Document 16 has disclosed a technique for controlling the excessreactivity with an electrolyte solution and improving fastcharge-discharge characteristics by heat-treating a spheroidized naturalgraphite in a nitrogen atmosphere at 500° C. to 1,250° C.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: JP 2000-340232 A

Patent Document 2: JP 2011-086617 A

Patent Document 3: JP 2005-50807 A

Patent Document 4: JP 2008-305722 A

Patent Document 5: JP 2014-114197 A

Patent Document 6: WO 2014/141372

Patent Document 7: JP 2010-251126 A

Patent Document 8: JP 2012-84520 A

Patent Document 9: JP 2012-074297 A

Patent Document 10: JP 2014-060148 A

Patent Document 11: JP 09-213328 A

Patent Document 12: WO 11/145178

Patent Document 14: JP 2003-297352 A

Patent Document 15: JP 2013-8526 A

Patent Document 16: JP 2010-135314 A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, the investigation by the present inventors has shown thatalthough the spheroidized natural graphites disclosed in Patent Document1 and Patent Document 2 provide a high capacity and good fastcharge-discharge characteristics as compared with the flake graphiteused as a raw material, these characteristics are still insufficient.This is because the spheroidized natural graphites have coarseintra-particle voids and structures lacking fineness, and thuselectrolyte solution cannot be smoothly and efficiently distributed intothe intra-particle voids, and Li-ion insertion/extraction sites in theparticles cannot be effectively used.

The isotropically pressurized spheroidized natural graphite disclosed inPatent Document 3, although providing a certain improvement in fastcharge-discharge characteristics, which is due to the smooth movement ofelectrolyte solution between electrodes resulting from fillingproperties improved by the increased density of the particles, providesinsufficient low-temperature output characteristics. This is becauseelectrolyte solution cannot penetrate into the particles as a result ofthe elimination of intra-particle voids, and Li-ion insertion/extractionsites in the particles cannot be efficiently used.

The spheroidized natural graphite disclosed in Patent Document 1,although providing a high capacity and good fast charge-dischargecharacteristics as compared with the flake graphite used as a rawmaterial, unfortunately provides low battery characteristics andproductivity because the particles poorly adhere to each other to causeresidual flake graphite and generate fine powder during thespheroidization.

The powdered carbon material disclosed in Patent Document 4 provides aninsufficient improvement in battery characteristics because the meltableorganic substance and the pitch contained during the spheroidization ofthe graphite contain softened solids, and thus the raw carbon materialspoorly adhere to each other, and residual flake graphite and thegeneration of fine powder during the spheroidization cannot be reduced.

The method for producing a spheroidized graphite disclosed in PatentDocument 5 also provides an insufficient improvement in batterycharacteristics because the addition of a resin binder hardly improvesthe adhesion between the graphite particles, and the generation of finepowder cannot be reduced. Although a method of spheroidization includingthe addition of a solution of the resin binder in toluene has also beendisclosed, the method requires further improvement because thetemperature during the spheroidization may exceed the low flash point ofthe solvent, which involves the risk of explosion or fire during theproduction.

Patent Document 6 has not disclosed a method of granulating a graphiteinto spheroidal particles, and, in addition, the method disclosedprovides an insufficient reduction in generation of fine powder duringthe spheroidization and an insufficient improvement in batterycharacteristics because paraffin wax is solid.

The carbon materials disclosed in Patent Documents 7 and 8 still containfine powder generated through the fracture of a raw flake graphiteduring the spheroidization, and the fine powder has a low bindingcapacity to parent particles. Thus, when a negative electrode isproduced using these carbon materials, a great amount of fine powder mayoccur, for example, upon physical impact, and non-aqueous secondarybatteries including these carbon materials may fail to provide asufficient input and output in initial and subsequent cycles.

Specifically, for the carbon material described in Patent Document 7,only the fine powder on the surface of a spheroidized natural graphitecontactable with the air is removed, and fine powder that generates uponphysical impact is difficult to remove. The treatment performed on thecarbon material described in Patent Document 8 can remove only the finepowder that increases the amount of micropore and can hardly remove finepowder that generates upon physical impact.

The carbon material described in Patent Document 2, which has afrequency of particles with a diameter of 5 μm or less, as measuredafter ultrasonic waves have been applied for 10 minutes, of 40% to 85%,can be considered to be a carbon material that generates a great amountof fine powder upon physical impact.

The investigation by the present inventors has shown that thespheroidized natural graphites disclosed in Patent Document 1 and PatentDocument 9 have a structure lacking particle fineness, a poor balancebetween a specific surface area and a tap density (also referred to astapping density), a small number of Li-ion insertion/extraction sites onparticles, and insufficient filling properties of negative electrode,and thus there is room for improvement in input-output characteristicsand increase in capacity of batteries.

The spheroidized natural graphite with carbon black deposited thereondisclosed in Patent Document 10, although providing a certainimprovement in input-output characteristics, which is due to the smoothmovement of electrolyte solution resulting from the fine structureformed on the particle surface, still has a poor balance between aspecific surface area and a tap density; there is room for improvementin input-output characteristics and increase in capacity of batteries.

The above-described improvement in input-output characteristics can beachieved, for example, by increasing the specific surface area of thecarbon material to improve the reactivity with an electrolyte solution.The increase in density of an active material layer for the increase incapacity can be achieved, for example, by increasing the tap density ofthe carbon material. The investigation by the present inventors hasrevealed that in the case of graphite particles having substantially thesame true density and average particle diameter, the tap densityincreases as the shape comes closer to spheroidal and the particlesurface becomes flat. In other words, to increase the tap density, it isimportant that the particle shape be rounded and closer to spheroidal,and the particle surface be made free from frays and chips and keptflat. A particle shape closer to spheroidal and a flat particle surfacesignificantly improves powder filling properties. However, there isusually a trade-off between the specific surface area and the tapdensity, and, unfortunately, increasing the specific surface areadecreases the tap density.

The investigation by the present inventors has shown that thespheroidized natural graphites disclosed in Patent Document 1 and PatentDocument 9 have a structure lacking particle fineness, and coating theparticle surface with amorphous carbon results in a reduced specificsurface area and a small number of Li-ion insertion/extraction sites onparticles; there is room for improvement in input-output characteristicsof batteries.

It is generally known that graphite particles having a large specificsurface area have a large number of Li-ion insertion/extraction sitesand thus provide a battery with improved input-output characteristics.

Meanwhile, a carbonaceous material coating on graphite particles hasshown to have a structure that has lower crystallinity than graphite andfacilitates Li-ion insertion/extraction and thus provide a battery withimproved input-output characteristics. That is to say, a large specificsurface area and graphite particles with reduced crystallinity canenhance input-output characteristics. However, the carbonaceous materialcoating on graphite particles for increasing the low-crystallinityregion that facilitates Li-ion insertion/extraction covers the finestructure of the particle surface; there is a trade-off between theincrease in specific surface area and the increase in low-crystallinityregion through the carbonaceous material coating.

The investigation by the present inventors has shown that although thecomposite graphites disclosed in Patent Documents 1 and 11, which aremade of a graphite and an amorphous carbon coating on the graphitesurface, can provide a high capacity and good fast charge-dischargecharacteristics as compared with the flake graphite or the spheroidizedgraphite particles used as a raw material, these characteristics arestill insufficient because the coating uniformity of the amorphouscarbon is not taken into account. For the composite carbon materialdisclosed in Patent Document 12, although exposed portions ofhigh-crystallinity carbonaceous particles having a microscopic Raman Rvalue of 0.2 or less are reduced by controlling the percentage of carbonmaterials having a microscopic Raman R value of 0.2 or larger to be atleast 20, the distribution and variation of microscopic Raman values,particularly, the distribution and variation of microscopic Raman valuesof particles having a large microscopic Raman R value, that is, thedegree of maldistribution of portions coated with low-crystallinitycarbon material is not taken into account, and the characteristics arestill insufficient. For the composite particles disclosed in PatentDocument 10, although particles having extremely large microscopic RamanR values and particles having extremely small values are not contained,the distribution and variation of microscopic Raman R values are nottaken into account, similarly to Patent Document 12, and thecharacteristics are still insufficient.

The investigation by the present inventors has shown that the techniquedisclosed in Patent Document 14 provides an improvement incharge-discharge efficiency through the use of an amorphous carbonhaving a controlled volume of pores of 0.33 nm to 0.40 nm but has adrawback in that the amorphous carbon is hard to densify for its smalltrue density and poor pressability.

The investigation by the present inventors has shown that the techniquedisclosed in Patent Document 15 using an isotropically pressurizedspheroidized natural graphite, although providing a certain improvementin fast charge-discharge characteristics, which is due to the smoothmovement of electrolyte solution between the particles resulting fromfilling properties improved by the increased density of the particles,provides insufficient low-temperature output characteristics. This isbecause electrolyte solution cannot penetrate into the particles as aresult of the elimination of intra-particle voids, and Li-ioninsertion/extraction sites in the particles cannot be efficiently used.

The investigation by the present inventors has shown that although thespheroidized natural graphite disclosed in Patent Document 16, which isheat treated in a nitrogen atmosphere at 500° C. to 1,250° C., haslow-temperature charge characteristics improved by the disorder ofsurface crystal structure, the characteristics are still insufficient.This is because the number of Li-ion insertion/extraction sites is stillinsufficient, and the increase of labile carbon layers resulting fromthe elimination of oxygen functional groups during the heat treatmentimpedes the smooth movement of Li ions.

The investigation by the present inventors has shown that although thegranulated natural graphites disclosed in Patent Document 1 and PatentDocument 2 provide a high capacity and good fast charge-dischargecharacteristics as compared with the flake graphite used as a rawmaterial, these characteristics are still insufficient because thenumber of Li-ion insertion/extraction sites inside the graphites issmall. Furthermore, side reactions with an electrolyte solutionfrequently occur due to the large amount of oxygen functional group,which disadvantageously results in the increase in irreversible capacityand gas generation.

Although the granulated natural graphite disclosed in Patent Document16, which is heat treated in a nitrogen atmosphere at 500° C. to 1,250°C., can reduce side reactions with an electrolyte solution due to thereduction in oxygen functional group and has low-temperature chargecharacteristics improved by the moderately disordered surface crystalstructure, the number of Li-ion insertion/extraction sites inside thegraphite is insufficient, and the characteristics are insufficient.

The technique in Patent Document 6, in which coal-derived calcined cokeis used as a raw material and granulated into spheroidal particles,provides a low discharge capacity, which is insufficient.

The investigation by the present inventors has shown that thespheroidized natural graphite disclosed in Patent Document 1, althoughproviding a high capacity and good fast charge-discharge characteristicsas compared with the flake graphite used as a raw material,unfortunately provides low battery characteristics and productivitybecause the particles poorly adhere to each other to cause residualflake graphite and generate fine powder during the spheroidization.

The powdered negative electrode material disclosed in Patent Document 4provides an insufficient improvement in battery characteristics becausethe meltable organic substance and the pitch contained during thespheroidization of the graphite contain softened solids, and thus theraw carbon materials poorly adhere to each other, and residual flakegraphite and the generation of fine powder during the spheroidizationcannot be reduced. Furthermore, since the affinity with the pitch is nottaken into account, the meltable organic substance contained during thespheroidization of the graphite cannot uniformly cover the carbonaceousmaterial and provides an insufficient improvement in batterycharacteristics also when used as a raw material of composite particlescontaining the resulting spheroidized graphite particles and acarbonaceous material.

The method for producing a spheroidized graphite disclosed in PatentDocument 5 also provides an insufficient improvement in batterycharacteristics because the addition of a resin binder hardly improvesthe adhesion between the graphite particles, and the generation of finepowder cannot be reduced. Although a method of spheroidization includingthe addition of a solution of the resin binder in toluene has also beendisclosed, the method requires further improvement because thetemperature during the spheroidization may exceed the low flash point ofthe solvent, which involves the risk of explosion or fire during theproduction. Furthermore, since the affinity with an organic substance,serving as a precursor of the carbonaceous material, is not taken intoaccount, the resin binder described cannot uniformly cover thecarbonaceous material and provides an insufficient improvement inbattery characteristics also when used as a raw material of compositeparticles containing the resulting spheroidized graphite particles and acarbonaceous material.

Patent Document 6 has not disclosed a method of granulating a graphiteinto spheroidal particles, and, in addition, the method disclosedprovides an insufficient reduction in generation of fine powder duringthe spheroidization and an insufficient improvement in batterycharacteristics because paraffin wax is solid. Furthermore, since theaffinity with an organic substance, serving as a precursor of thecarbonaceous material, is not taken into account, the paraffin waxcannot uniformly cover the carbonaceous material and provides aninsufficient improvement in battery characteristics also when used as araw material of composite particles containing the resulting granulatedparticles and a carbonaceous material.

Although the composite graphites disclosed in Patent Documents 1 and 11to 12, which are made of a graphite and an amorphous carbon coating onthe graphite surface, can provide a high capacity and good fastcharge-discharge characteristics as compared with the flake graphite orthe spheroidized graphite particles used as a raw material, thesecharacteristics are still insufficient because the relationship betweenthe tap density, the true density, and the density under a load of thegraphite is not taken into account.

The present invention has been made in view of the above circumstances,and an object (object A) of the present invention is to provide a carbonmaterial that can provide a non-aqueous secondary battery having a highcapacity of 355 mAh/g or more, for example, and excellent input-outputcharacteristics (low-temperature output characteristics) and, as aresult, provide a high-performance non-aqueous secondary battery.

Another object (object B) of the present invention is to provide amethod for producing a carbon material for a non-aqueous secondarybattery, comprising the step of granulating a raw carbon material. Themethod can produce carbon materials for non-aqueous secondary batterieshaving various types of particle structures and can stably producecarbon materials that can be processed in bulk, have a high degree ofspheroidization, good filling properties, and low anisotropy, andgenerate little amount of fine powder. A still another object is toprovide a carbon material that can provide a non-aqueous secondarybattery having a high capacity of 355 mAh/g or more, for example, andexcellent input-output characteristics (low-temperature outputcharacteristics) by this method and, as a result, provide ahigh-performance non-aqueous secondary battery.

Means for Solving the Problems

The inventors have intensively studied to achieve the object A todiscover that a carbon material for a non-aqueous secondary battery,comprising a graphite capable of occluding and releasing lithium ions,the carbon material having a cumulative pore volume at pore diameters ina range of 0.01 μm to 1 μm of 0.08 mL/g or more, a roundness, asdetermined by flow-type particle image analysis, of 0.88 or greater, anda ratio (PD/d50(%)) of mode pore diameter (PD) in a pore diameter rangeof 0.01 μm to 1 μm in a pore distribution determined by mercuryintrusion to volume-based average particle diameter (d50) of 1.8 or lesscan provide a non-aqueous secondary battery negative electrode materialhaving a high capacity and excellent low-temperature outputcharacteristics and cycle characteristics, thereby completing InventionA.

More specific aspects of Invention A are as follows:

(A1) A carbon material for a non-aqueous secondary battery, comprising agraphite capable of occluding and releasing lithium ions, the carbonmaterial having a cumulative pore volume at pore diameters in a range of0.01 μm to 1 μm of 0.08 mL/g or more, a roundness, as determined byflow-type particle image analysis, of 0.88 or greater, and a porediameter to particle diameter ratio (PD/d50(%)) of 1.8 or less, theratio being given by equation (1A):

PD/d50(%)=mode pore diameter (PD) in a pore diameter range of 0.01 μm to1 μm in a pore distribution determined by mercury intrusion/volume-basedaverage particle diameter (d50)×100  (1A).

(A2) A carbon material for a non-aqueous secondary battery capable ofoccluding and releasing lithium ions, the carbon material being formedfrom a plurality of graphite particles without being pressed and havinga pore diameter to particle diameter ratio (PD/d50(%) of 1.8 or less,the ratio being given by equation (1A):

PD/d50(%)=mode pore diameter (PD) in a range of 0.01 μm to 1 μm in apore distribution determined by mercury intrusion/volume-based averageparticle diameter (d50)×100  (1A).

(A3) The carbon material for a non-aqueous secondary battery accordingto (A1) or (A2), wherein the carbon material is a spheroidized graphitemade of flake graphite, crystalline graphite, and vein graphite and hasa half width at half maximum of pore distribution (log (nm)) of 0.45 orgreater,

the half width at half maximum of pore distribution (log (nm)) referringto a half width at half maximum at a micropore side of a peak in a porediameter range of 0.01 μm to 1 μm in a pore distribution (nm), asdetermined by mercury intrusion (mercury porosimetry), of the carbonmaterial for a non-aqueous secondary battery, with a horizontal axisexpressed in common logarithm (log (nm)).

(A4) The carbon material for a non-aqueous secondary battery accordingto (A1) or (A2), wherein the carbon material is a composite carbonmaterial comprising a spheroidized graphite made of flake graphite,crystalline graphite, and vein graphite and a carbonaceous material andhas a half width at half maximum of pore distribution (log (nm)) of 0.3or greater,

the half width at half maximum of pore distribution (log (nm)) referringto a half width at half maximum at a micropore side of a peak in a porediameter range of 0.01 μm to 1 μm in a pore distribution (nm), asdetermined by mercury intrusion (mercury porosimetry), of the carbonmaterial for a non-aqueous secondary battery, with a horizontal axisexpressed in common logarithm (log (nm)).

(A5) The carbon material for a non-aqueous secondary battery accordingto any one of (A1) to (A4), wherein the carbon material is aspheroidized graphite made of flake graphite.(A6) The carbon material for a non-aqueous secondary battery accordingto any one of (A1) to (A5), wherein the carbon material has a frequencyof particles with a particle diameter of 3 μm or less of 1% to 60%, theparticle diameter and the frequency of particles being measured using aflow-type particle image analyzer after the carbon material has beenirradiated with ultrasonic waves of 28 kHz at a power of 60 W for 5minutes.(A7) A non-aqueous secondary battery comprising:

a positive electrode and a negative electrode, each being capable ofoccluding and releasing lithium ions; and

an electrolyte,

the negative electrode comprising a current collector and a negativeelectrode active material layer on the current collector, the negativeelectrode active material layer comprising the carbon material accordingto any one of (A1) to (A6).

The inventors have intensively studied to achieve the object B to find

A method for producing a carbon material for a non-aqueous secondarybattery, comprising

a granulation step of granulating a raw carbon material by applying atleast one type of mechanical energy selected from impact, compression,friction, and shear force, the step of granulating a raw carbon materialbeing carried out in the presence of a granulating agent that satisfiesconditions 1) and 2):

1) being liquid during the step of granulating the raw carbon material;and

2) in the granulating agent, no organic solvent is contained, or ifcontained, at least one of the organic solvents has no flash point or aflash point of 5° C. or higher.

More specific aspects of Invention B are as follows:

(B1) A method for producing a carbon material for a non-aqueoussecondary battery, comprising

a granulation step of granulating a raw carbon material by applying atleast one type of mechanical energy selected from impact, compression,friction, and shear force, the granulation step being carried out in thepresence of a granulating agent that satisfies conditions 1) and 2):

1) being liquid during the step of granulating the raw carbon material;and

2) in the granulating agent, no organic solvent is contained, or ifcontained, at least one of the organic solvents has no flash point or aflash point of 5° C. or higher.

(B2) The production method according to (B1), wherein the granulatingagent has a contact angle θ with a graphite of less than 90°, thecontact angle being measured by the following method:Method for Measuring Contact Angle θ with Graphite

Onto a surface of HOPG, 1.2 μL of a granulating agent is added dropwise,and when wetting and spreading has settled down and a rate of change incontact angle θ of the granulating agent added dropwise in one secondhas reached 3% or lower, the contact angle is measured using a contactangle meter (DM-501 automatic contact angle meter available from KyowaInterface Science Co., Ltd). When a granulating agent having a viscosityat 25° C. of 500 cP or lower is used, a value at 25° C. is employed as ameasurement of the contact angle θ, and when a granulating agent havinga viscosity at 25° C. of higher than 500 cP is used, a value at anincreased temperature where the viscosity is not higher than 500 cP isemployed.

(B3) The production method according to (B1) or (B2), wherein thegranulating agent has a viscosity of 1 cP or more during the granulationstep.(B4) The production method according to any one of (B1) to (B3), whereinthe granulating agent has a viscosity at 25° C. of 1 cP to 100,000 cP.(B5) The production method according to any one of (B1) to (B4), whereinthe raw carbon material comprises at least one selected from the groupconsisting of flake, crystalline, and vein natural graphites.(B6) The production method according to any one of (B1) to (B5), whereinthe raw carbon material has a d₀₀₂ of 0.34 nm or less.(B7) The production method according to any one of (B1) to (B6), whereinthe granulation step comprises granulating the raw carbon material inthe presence of at least one selected from the group consisting ofmetals capable of forming alloys with Li, oxides thereof, amorphouscarbon, and green coke.(B8) The production method according to any one of (B1) to (B7), whereinthe granulation step is carried out in an atmosphere at 0° C. to 250° C.(B9) The production method according to any one of (B1) to (B8), whereinthe granulation step comprises placing the graphite in an apparatuscomprising a rotatable member that rotates at a high speed in a casingand having a rotor equipped with a plurality of blades in the casing,and applying any one of impact, compression, friction, and shear forceto the graphite placed in the apparatus by rotating the rotor at a highspeed.(B10) The production method according to any one of (B1) to (B9),further comprising the step of depositing a carbonaceous material havinglower crystallinity than the raw carbon material on the granulatedcarbon material obtained in the granulation step.

The inventors have intensively studied to achieve the object A to findanother object, that is, to achieve a carbon material for a non-aqueoussecondary battery having so high particle strength as to generate littleamount of fine powder even upon physical impact, and discovered thatusing a carbon material for a non-aqueous secondary battery capable ofoccluding and releasing lithium ions and formed from a plurality ofgraphite particles as a negative electrode active material, the carbonmaterial satisfying inequality (1C):

Q _(5min)(%)/D50 (μm)≦3.5  (1C)

where Q_(5min) (%) is a frequency (%) of particles with a diameter of 5μm or less measured using a flow-type particle image analyzer after thecarbon material has been irradiated with ultrasonic waves of 28 kHz at apower of 60 W for 5 minutes; andD50 (μm) is a volume-based median diameter determined by laserdiffraction/scattering after the carbon material has been irradiatedwith ultrasonic waves of 28 kHz at a power of 60 W for 1 minute,can provide a non-aqueous secondary battery having excellentinput-output characteristics and excellent cycle characteristics,thereby completing Invention C.

More specific aspects of Invention C are as follows:

(C1) A carbon material for a non-aqueous secondary battery capable ofoccluding and releasing lithium ions and formed from a plurality ofgraphite particles, the carbon material satisfying inequality (1C):

Q _(5min)(%)/D50 (μm)≦3.5  (1C)

where Q_(5min) (%) is a frequency (%) of particles with a diameter of 5μm or less measured using a flow-type particle image analyzer after thecarbon material has been irradiated with ultrasonic waves of 28 kHz at apower of 60 W for 5 minutes; andD50 (μm) is a volume-based median diameter determined by laserdiffraction/scattering after the carbon material has been irradiatedwith ultrasonic waves of 28 kHz at a power of 60 W for 1 minute.(C2) The carbon material for a non-aqueous secondary battery accordingto (C1), wherein the carbon material has a Q_(5min) (%) of 40% or less.(C3) The carbon material for a non-aqueous secondary battery accordingto (C1) or (C2), wherein the total amount of eliminated CO andeliminated CO₂, as measured using a pyrolysis mass spectrometer (TPD-MS)by heating the carbon material from room temperature to 1,000° C., is125 μmol/g or less.(C4) The carbon material for a non-aqueous secondary battery accordingto any one of (C1) to (C3), wherein the amount of eliminated CO, asmeasured using a pyrolysis mass spectrometer (TPD-MS) by heating thecarbon material from room temperature to 1,000° C., is 100 μmol/g orless.(C5) The carbon material for a non-aqueous secondary battery accordingto any one of (C1) to (C4), wherein the amount of eliminated CO₂ asmeasured using a pyrolysis mass spectrometer (TPD-MS) by heating thecarbon material from room temperature to 1,000° C., is 25 μmol/g orless.(C6) The carbon material for a non-aqueous secondary battery accordingto any one of (C1) to (C5), wherein the carbon material has a tapdensity of 0.7 g/cm³ to 1.3 g/cm³.(C7) The carbon material for a non-aqueous secondary battery accordingto any one of (C1) to (C6), wherein the carbon material has a roundnessof 0.86 or greater.(C8) The carbon material for a non-aqueous secondary battery accordingto any one of (C1) to (C7), wherein the carbon material has a BETspecific surface area of 2 m²/g to 30 m²/g.(C9) The carbon material for a non-aqueous secondary battery accordingto any one of (C1) to (C8), wherein the carbon material has avolume-based median diameter (D50) of 1 μm to 50 μm.(C10) The carbon material for a non-aqueous secondary battery accordingto any one of (C1) to (C9), wherein the carbon material has an Lc of 90nm or more and a d₀₀₂ of 0.337 nm or less, the values being determinedby wide-angle X-ray diffractometry.(C11) The carbon material for a non-aqueous secondary battery accordingto any one of (C1) to (C10), wherein the graphite particles contain anatural graphite.(C12) A composite carbon material for a non-aqueous secondary battery,comprising

the carbon material according to any one of (C1) to (C11); and

a carbonaceous material combined with the carbon material.(C13) A non-aqueous lithium ion secondary battery comprising:

a positive electrode and a negative electrode, each being capable ofoccluding and releasing lithium ions; and

an electrolyte,

the negative electrode comprising the carbon material for a non-aqueoussecondary battery according to any one of (C1) to (C11) or the compositecarbon material for a non-aqueous secondary battery according to (C12).

The inventors have intensively studied to achieve the object A todiscover that a carbon material for a non-aqueous secondary batterycapable of occluding and releasing lithium ions, the carbon materialcomprising a carbonaceous material on a particle surface and having atap density and a specific surface area (SA) determined by BET methodsatisfying a specific relationship, can provide a non-aqueous secondarybattery negative electrode material having a high capacity and excellentinput-output characteristics and cycle characteristics, therebycompleting Invention D.

More specific aspects of Invention D are as follows:

(D1) A carbon material for a non-aqueous secondary battery capable ofoccluding and releasing lithium ions, the carbon material comprising acarbonaceous material on a particle surface and satisfying therelationship of inequality (1D):

10Y _(d)+0.26X _(d)≧α  (1D)

(Y_(d)=tap density (g/cm³), X_(d)=specific surface area (SA) (m²/g) ofcarbon material determined by BET method, α=12.60).(D2) The carbon material for a non-aqueous secondary battery accordingto (D1), wherein the specific surface area (SA) (m²/g) of the carbonmaterial determined by BET method is 2 or greater.(D3) The carbon material for a non-aqueous secondary battery accordingto (D1) or (D2), wherein the carbon material comprises a plurality ofgraphites selected from the group consisting of at least one of flakegraphite, crystalline graphite, and vein graphite.(D4) The carbon material for a non-aqueous secondary battery accordingto any one of (D1) to (D3), wherein the carbon material has a 1stdischarge capacity of 300 mAh/g or more.(D5) A non-aqueous secondary battery comprising

a positive electrode and a negative electrode, each being capable ofoccluding and releasing lithium ions; and

an electrolyte,

the negative electrode comprising a current collector and a negativeelectrode active material layer on the current collector, the negativeelectrode active material layer comprising the carbon material accordingto any one of (D1) to (D4).

The inventors have intensively studied to achieve the object A to findanother object, that is, to provide a carbon material for a non-aqueoussecondary battery overcoming the traditional trade-off between specificsurface area and low-crystallinity region and having excellentinput-output characteristics, and discovered that a carbon material fora non-aqueous secondary battery capable of occluding and releasinglithium ions, the carbon material comprising a carbonaceous material ona particle surface and having a true density and a specific surface area(SA) determined by BET method satisfying a specific relationship, canprovide a carbon material for a non-aqueous secondary battery havingexcellent input-output characteristics, thereby completing Invention E.The true density is a physical property that indicates the crystallinityof graphite particles.

More specific aspects of Invention E are as follows:

(E1) A carbon material for a non-aqueous secondary battery capable ofoccluding and releasing lithium ions, the carbon material comprising acarbonaceous material on a particle surface and satisfying therelationship of inequality (1E):

Y _(e)−0.01X _(e)≦α  (1E)

(Y_(e)=true density (g/cm³), X_(e)=specific surface area (SA) (m²/g) ofcarbon material determined by BET method, α=2.20).(E2) The carbon material for a non-aqueous secondary battery accordingto (E1), wherein the specific surface area (SA) (m²/g) of the carbonmaterial determined by BET method is 2 or greater.(E3) The carbon material for a non-aqueous secondary battery accordingto (E1) or (E2), wherein the carbon material comprises a plurality ofgraphites selected from the group consisting of at least one of flakegraphite, crystalline graphite, and vein graphite.(E4) The carbon material for a non-aqueous secondary battery accordingto any one of (E1) to (E3), wherein the carbon material has a 1stdischarge capacity of 300 mAh/g or more.(E5) The carbon material for a non-aqueous secondary battery accordingto any one of (E1) to (E4), wherein the carbon material has a 90%particle diameter (d90) to 10% particle diameter (d10) ratio (d90/d10)in a volume-based particle size distribution of 2.6 or greater.(E6) A non-aqueous secondary battery comprising:

a positive electrode and a negative electrode, each being capable ofoccluding and releasing lithium ions; and

an electrolyte, the negative electrode comprising a current collectorand a negative electrode active material layer on the current collector,the negative electrode active material layer comprising the carbonmaterial according to any one of (E1) to (E5).

The inventors have intensively studied to achieve the object A todiscover that a composite carbon material comprising a carbon material(A) capable of occluding and releasing lithium ions (hereinafter alsoreferred to as “the carbon material (A)”) and a carbonaceous material(B) on the surface of the carbon material (A) (hereinafter also referredto as “the composite carbon material”), wherein the average value ofmicroscopic Raman R values of 30 randomly selected composite carbonmaterials is 0.1 to 0.85, and the standard deviation (σ_(R)) is 0.1 orless, can provide a non-aqueous secondary battery negative electrodematerial having a high capacity and excellent low-temperature outputcharacteristics and cycle characteristics, thereby completing InventionF.

More specific aspects of Invention F are as follows:

(F1) A composite carbon material comprising:

a carbon material (A) capable of occluding and releasing lithium ions:and

a carbonaceous material (B) on the surface of the carbon material (A),

wherein the average value of microscopic Raman R values of 30 randomlyselected composite carbon materials is 0.1 to 0.85, and the standarddeviation (σ_(R)) is 0.1 or less.

(F2) The composite carbon material for a non-aqueous secondary batteryaccording to (F1), wherein the composite carbon material has amicroscopic Raman R₁₅ value of 12% or less, the value being given byequation (1F):

Microscopic Raman R ₍₁₅₎ value (%)=the number of composite carbonmaterials having a microscopic Raman R value of 0.15 or less among 30randomly selected composite carbon materials/30×100  (1F).

(F3) The composite carbon material for a non-aqueous secondary batteryaccording to (F1) or (F2), wherein the composite carbon material has atap density of 0.6 g/cm³ to 1.20 g/cm³.(F4) The composite carbon material for a non-aqueous secondary batteryaccording to any one of (F1) to (F3), wherein the composite carbonmaterial has a specific surface area (SA) of 1 m²/g to 30 m²/g.(F5) The composite carbon material for a non-aqueous secondary batteryaccording to any one of (F1) to (F4), wherein the carbon material is aspheroidized graphite made of at least one carbon material selected fromthe group consisting of flake natural graphite, crystalline naturalgraphite, and vein natural graphite.(F6) A method for producing a composite carbon material for anon-aqueous secondary battery, comprising:

mixing a carbon material having a cumulative pore volume in a range of0.01 μm to 1 μm of 0.07 mL/g or more and a pore diameter to particlediameter ratio (PD/d50(%)), as given by equation (2F), of 1.8 or lesswith a carbonaceous material precursor at a temperature equal to orhigher than a softening point of the carbonaceous material precursor;and then

carbonizing the carbonaceous material precursor by heat treatment.

PD/d50(%)=mode pore diameter (PD) in a range of 0.01 μm to 1 μm in apore distribution determined by mercury intrusion/volume-based averageparticle diameter (d50)×100  (2F)

(F7) The method for producing a composite carbon material for anon-aqueous secondary battery according to (F6), wherein the carbonmaterial is a spheroidized graphite made of at least one carbon materialselected from the group consisting of flake natural graphite,crystalline natural graphite, and vein natural graphite.(F8) The method for producing a composite carbon material for anon-aqueous secondary battery according to (F6) or (F7), wherein thecarbonaceous material precursor has a softening point of 400° C. orlower.(F9) A composite carbon material for a non-aqueous secondary batteryproduced by the method for producing a composite carbon material for anon-aqueous secondary battery according to any one of (F6) to (F8).(F10) A non-aqueous secondary battery comprising:

a positive electrode and a negative electrode, each being capable ofoccluding and releasing lithium ions; and

an electrolyte, the negative electrode comprising a current collectorand a negative electrode active material layer on the current collector,the negative electrode active material layer comprising the compositecarbon material according to any one of (F1) to (F5) and (F9).

The inventors have intensively studied to achieve the object A todiscover that a carbon material having specific values of a cumulativepore volume at pore diameters in a range of 2 to 4 nm and a tap densityimproves low-temperature output characteristics, thereby completingInvention G.

More specific aspects of Invention G are as follows:

(G1) A carbon material for a non-aqueous secondary battery capable ofoccluding and releasing lithium ions, the carbon material having acumulative pore volume at pore diameters in a range of 2 to 4 nm, asdetermined by nitrogen gas adsorption, of 0.0022 cm³/g or more and a tapdensity of 0.83 g/cm³ or more.(G2) The carbon material for a non-aqueous secondary battery accordingto (G1), wherein the carbon material has a maximum dV/dlog (D) (V:cumulative pore volume, D: pore diameter) at pore diameters in a rangeof 2 to 4 nm, as determined by nitrogen gas adsorption, of 0.0090 cm³/gor more.(G3) The carbon material for a non-aqueous secondary battery accordingto (G1) or (G2), wherein the carbon material has a cumulative porevolume at pore diameters in a range of 2 to 100 nm of 0.025 cm³/g ormore.(G4) The carbon material for a non-aqueous secondary battery accordingto any one of (G1) to (G3), wherein the carbon material comprises aplurality of graphites selected from the group consisting of at leastone of flake graphite, crystalline graphite, and vein graphite.(G5) A non-aqueous secondary battery comprising:

a positive electrode and a negative electrode, each being capable ofoccluding and releasing lithium ions; and

an electrolyte, the negative electrode comprising a current collectorand a negative electrode active material layer on the current collector,the negative electrode active material layer comprising the carbonmaterial according to any one of (G1) to (G5).

The inventors have intensively studied to achieve the object A todiscover that a carbon material for a non-aqueous secondary batterycapable of occluding and releasing lithium ions, the carbon materialhaving a Raman R value given by the following equation 1H and a thermalweight loss ratio per unit area (ΔTG/SA) in specific ranges, can providea non-aqueous secondary battery negative electrode material having ahigh capacity and excellent low-temperature output characteristics andcycle characteristics, thereby completing Invention H.

More specific aspects of Invention H are as follows:

(H1) A carbon material for a non-aqueous secondary battery capable ofoccluding and releasing lithium ions, the carbon material having a RamanR value, as given by equation (1H), of 0.31 or greater and a thermalweight loss ratio per unit area (ΔTG/SA), as given by equation (2H), of0.05 to 0.45.

Raman value R=intensity I _(B) of peak P _(B) near 1,360 cm⁻¹/intensityI _(A) of peak P _(A) near 1,580 cm⁻¹ by Raman spectrumanalysis  Equation (1H)

(ΔTG/SA)=(thermal weight loss (ΔTG) (%) on heating from 400° C. to 600°C. at 2° C./min in air atmosphere, measured with differential thermalbalance)/(specific surface area (SA) (m²/g) of carbon materialdetermined by BET method)  Equation (2H)

(H2) The carbon material for a non-aqueous secondary battery accordingto (H1), wherein the carbon material is a spheroidized graphite made offlake graphite, crystalline graphite, and vein graphite.(H3) The carbon material for a non-aqueous secondary battery accordingto (H1) or (H2), wherein the carbon material has a roundness, asdetermined by flow-type particle image analysis, of 0.88 or greater.(H4) A non-aqueous secondary battery comprising:

a positive electrode and a negative electrode, each being capable ofoccluding and releasing lithium ions; and

an electrolyte,

the negative electrode comprising a current collector and a negativeelectrode active material layer on the current collector, the negativeelectrode active material layer comprising the carbon material accordingto any one of (H1) to (H3).

The inventors have intensively studied to achieve the object A todiscover that a carbon material for a non-aqueous secondary batterycapable of occluding and releasing lithium ions, the carbon materialbeing graphite particles satisfying the relationship of inequality (1I),can provide a non-aqueous secondary battery negative electrode materialhaving a high capacity and excellent low-temperature outputcharacteristics and cycle characteristics, thereby completing InventionI.

100Y _(i)+0.26X _(i)>α  Inequality (1I)

(In inequality (1I), Y_(i) is an oxygen functional group dispersitygiven by equation (2I); X_(i) is a volume-based average particlediameter (d50) (μm); and α=9.4)

Oxygen functional group dispersity (Y _(i))=total oxygen content (mol %)determined by elemental analysis/surface oxygen content (O/C) (mol %)determined by X-ray photoelectron spectroscopy  Equation (2I)

More specific aspects of Invention I are as follows:

(I₁) A carbon material for a non-aqueous secondary battery capable ofoccluding and releasing lithium ions, the carbon material being graphiteparticles satisfying the relationship of inequality (1I).

100Y _(i)+0.26X _(i)≧α  Inequality (1I)

(In inequality (1I), Y_(i) is an oxygen functional group dispersitygiven by equation (2I); X_(i) is a volume-based average particlediameter (d50) (μm); and α=9.4)

Oxygen functional group dispersity (Y _(i))=total oxygen content (mol %)determined by elemental analysis/surface oxygen content (O/C) (mol %)determined by X-ray photoelectron spectroscopy  Equation (2I)

(I₂) The carbon material for a non-aqueous secondary battery accordingto (I₁), wherein the surface oxygen content (O/C) determined by X-rayphotoelectron spectroscopy is 2 mol % or less.(I₃) The carbon material for a non-aqueous secondary battery accordingto any one of (I₁) or (I2), wherein the carbon material has a Tapdensity of 0.7 g/cm³ or more.(I4) The carbon material for a non-aqueous secondary battery accordingto any one of (I1) to (I3), wherein the carbon material has a roundness,as determined by flow-type particle image analysis, of 0.88 or greater.(I5) The carbon material for a non-aqueous secondary battery accordingto any one of (I1) to (I4), wherein the graphite particles arespheroidal graphite particles formed by granulation of flake graphite,crystalline graphite, and vein graphite.(I6) The carbon material for a non-aqueous secondary battery accordingto any one of (I1) to (I5), wherein the granulation is carried out byapplying at least one type of mechanical energy selected from impact,compression, friction, and shear force.(I7) The carbon material for a non-aqueous secondary battery accordingto any one of (I1) to (I6), wherein the granulation is carried out byplacing the graphite in an apparatus comprising a rotatable member thatrotates at a high speed in a casing and having a rotor equipped with aplurality of blades in the casing, and applying any one of impact,compression, friction, and shear force to the graphite placed in theapparatus by rotating the rotor at a high speed.(I8) A non-aqueous secondary battery comprising:

a positive electrode and a negative electrode, each being capable ofoccluding and releasing lithium ions; and

an electrolyte,

the negative electrode comprising a current collector and a negativeelectrode active material layer on the current collector, the negativeelectrode active material layer comprising the carbon material accordingto any one of (I1) to (I7).

The inventors have intensively studied to achieve the object B to findanother object, that is, to provide a method for producing compositeparticles for a non-aqueous secondary battery, comprising spheroidallygranulated graphite particles having a structure in which fine powderhaving a great number of Li-ion insertion/extraction sites exists on andin the particles, the graphite particles being uniformly coated with acarbonaceous material, and discovered that a production methodcomprising:

1) applying at least one type of mechanical energy selected from impact,compression, friction, and shear force in the presence of a granulatingagent having an aniline point of 80° C. or lower or no aniline point togranulate a raw carbon material; and

2) mixing the granulated carbon material particles obtained in 1) withan organic compound, serving as a carbonaceous material precursor, andheat-treating the mixture,

thereby completing Invention J.

More specific aspects of Invention J are as follows:

(J1) A method for producing composite particles for a non-aqueoussecondary battery comprising a granulated carbon material and acarbonaceous material having lower crystallinity than the granulatedcarbon material, the method comprising the steps of 1) and 2):

1) applying at least one type of mechanical energy selected from impact,compression, friction, and shear force in the presence of a granulatingagent having an aniline point of 80° C. or lower or no aniline point togranulate a raw carbon material; and

2) mixing the granulated carbon material obtained in 1) with an organiccompound, serving as a carbonaceous material precursor, andheat-treating the mixture.

(J2) The method for producing composite particles for a non-aqueoussecondary battery according to (J1), wherein the granulating agent is anorganic compound having an aromatic ring and is liquid at 25° C.(J3) The method for producing composite particles for a non-aqueoussecondary battery according to (J1) or (J2), wherein the organiccompound, serving as a carbonaceous material precursor, comprises anorganic compound having an aromatic ring.(J4) The method for producing composite particles for a non-aqueoussecondary battery according to any one of (J1) to (J3), wherein theorganic compound, serving as a carbonaceous material precursor, is acoal-derived raw oil.(J5) The method for producing composite particles for a non-aqueoussecondary battery according to any one of (J1) to (J4), wherein the rawcarbon material particles comprise at least one selected from the groupconsisting of flake, crystalline, and vein natural graphites.(J6) The method for producing composite particles for a non-aqueoussecondary battery according to any one of (J1) to (J5), wherein the rawcarbon material has a d₀₀₂ of 0.34 nm or less.(J7) The method for producing composite particles for a non-aqueoussecondary battery according to any one of (J1) to (J6), wherein thegranulation step is carried out in an atmosphere at 0° C. to 250° C.(J8) The method for producing composite particles for a non-aqueoussecondary battery according to any one of (J1) to (J7), wherein thegranulation step comprises placing the graphite in an apparatuscomprising a rotatable member that rotates at a high speed in a casingand having a rotor equipped with a plurality of blades in the casing,and applying any one of impact, compression, friction, and shear forceto the graphite placed in the apparatus by rotating the rotor at a highspeed.(J9) Composite particles for a non-aqueous secondary battery produced bythe production method according to any one of (J1) to (J8).(J10) A non-aqueous secondary battery comprising:

a positive electrode and a negative electrode, each being capable ofoccluding and releasing lithium ions; and

an electrolyte,

the negative electrode comprising a current collector and a negativeelectrode active material layer on the current collector, the negativeelectrode active material layer comprising the composite particles for anon-aqueous secondary battery according to (J9).

The inventors have intensively studied to achieve the object A todiscover that while the reasons are not fully understood, a carbonmaterial having a true density that satisfies a specific relationshipwith a density under a specific load minus a tap density can provide acarbon material for a non-aqueous secondary battery negative electrodehaving a high capacity and excellent low-temperature outputcharacteristics, thereby completing Invention K.

More specific aspects of Invention K are as follows:

(K1) A carbon material for a non-aqueous secondary battery, satisfyinginequality (1K).

10.914>5x _(k) −y _(k)−0.0087a  Inequality (1K)

(In inequality (1K), x_(k) is a true density [g/cm³] of the carbonmaterial; y_(k) is a value determined by equation (2K); and a is avolume-based average particle diameter [μm] of the carbon material.)

y _(k)=(density [g/cm³] of carbon material under uniaxial load of 100kgf/3.14 cm²)−(tap density of carbon material [g/cm³])  Equation (2K)

(K2) A carbon material for a non-aqueous secondary battery, satisfyinginequality (3K).

10.990>5x _(k) −y _(k)  Inequality (3K)

(In inequality (3K), x_(k) is a true density [g/cm³] of the carbonmaterial, and y_(k) is a value determined by equation (2K).)

y _(k)=(density [g/cm³] of powder carbon material under uniaxial load of100 kgf/3.14 cm²)−(tap density of carbon material [g/cm³])  Equation(2K)

(K3) The carbon material for a non-aqueous secondary battery accordingto (K1) or (K2), wherein the carbon material has a true density of 2.20g/cm³ to 2.262 g/cm³.(K4) The carbon material for a non-aqueous secondary battery accordingto any one of (K1) to (K3), wherein the carbon material has a tapdensity of 0.85 g/cm³ or more.(K5) The carbon material for a non-aqueous secondary battery accordingto any one of (K1) to (K4), wherein at least part of the surface of thecarbon material is coated with an amorphous carbon.(K6) The carbon material for a non-aqueous secondary battery accordingto any one of (K1) to (K4), wherein the carbon material comprisesspheroidal graphite particles formed by granulation of flake graphite,crystalline graphite, and vein graphite.(K7) The carbon material for a non-aqueous secondary battery accordingto (K6), wherein the granulation is carried out by applying at least onetype of mechanical energy selected from impact, compression, friction,and shear force.(K8) The carbon material for a non-aqueous secondary battery accordingto (K6) or (K7), wherein the granulation is carried out by placing thegraphite in an apparatus comprising a rotatable member that rotates at ahigh speed in a casing and having a rotor equipped with a plurality ofblades in the casing, and applying any one of impact, compression,friction, and shear force to the graphite placed in the apparatus byrotating the rotor at a high speed.(K9) A non-aqueous secondary battery comprising:

a positive electrode and a negative electrode, each being capable ofoccluding and releasing lithium ions; and

an electrolyte,

the negative electrode comprising a current collector and a negativeelectrode active material layer on the current collector, the negativeelectrode active material layer comprising the carbon material accordingto any one of (K1) to (K8).

The inventors have intensively studied to achieve the object A todiscover that fining intra-particle pores (L¹), uniformly dispersingintra-particle pores (L²), or controlling the orientation of and theinterval between intra-particle voids (L³) can provide a non-aqueoussecondary battery negative electrode material having a high capacity andexcellent low-temperature output characteristics and cyclecharacteristics, thereby completing Inventions L (L¹ to L³).

More specifically, aspects of Invention L¹ are as follows:

(L¹1) A carbon material for a non-aqueous secondary battery, comprisinggranulated particles satisfying (1L) and (2L):

the carbon material for a non-aqueous secondary battery having anaverage box-counting dimension relative to void regions of 30 particlesof 1.55 or greater, as calculated from images obtained by randomlyselecting 30 granulated particles from a cross-sectional SEM image ofthe carbon material for a non-aqueous secondary battery, dividing thecross-sectional SEM image of each granulated particle into void regionsand non-void regions, and binarizing the image.

(1L) The granulated particles are made of a carbonaceous material; and(2L) The granulated particles satisfy the relationship |X₁−X|/X₁≦0.2,where X is a volume-based average particle diameter determined by laserdiffraction, and X₁ is an equivalent circular diameter as determinedfrom a cross-sectional SEM image,

provided that the cross-sectional SEM image is a reflected electronimage acquired at an acceleration voltage of 10 kV.

(L¹ ₂) The carbon material for a non-aqueous secondary battery accordingto (L¹1), wherein the granulated particles satisfy the relationship|R−R₁|≦0.1, where R is a roundness determined with a flow-type particleimage analyzer, and R₁ is a roundness determined from a cross-sectionalSEM image.(L¹3) The carbon material for a non-aqueous secondary battery accordingto (L¹1) or (L¹2), wherein the carbon material has a tap density of 0.7g/cm³ or more.(L¹4) The carbon material for a non-aqueous secondary battery accordingto any one of (L¹1) to (L¹3), wherein the carbon material has aroundness, as determined by flow-type particle image analysis, of 0.88or greater.(L¹5) The carbon material for a non-aqueous secondary battery accordingto any one of (L¹1) to (L¹4), wherein the graphite particles arespheroidal graphite particles formed by granulation of flake graphite,crystalline graphite, and vein graphite.(L¹6) The carbon material for a non-aqueous secondary battery accordingto any one of (L¹1) to (L¹5), wherein the granulation is carried out byapplying at least one type of mechanical energy selected from impact,compression, friction, and shear force.(L¹7) The carbon material for a non-aqueous secondary battery accordingto any one of (L¹1) to (L¹6), wherein the granulation is carried out byplacing the graphite in an apparatus comprising a rotatable member thatrotates at a high speed in a casing and having a rotor equipped with aplurality of blades in the casing, and applying any one of impact,compression, friction, and shear force to the graphite placed in theapparatus by rotating the rotor at a high speed.(L¹8) A non-aqueous secondary battery comprising:

a positive electrode and a negative electrode, each being capable ofoccluding and releasing lithium ions; and

an electrolyte,

the negative electrode comprising a current collector and a negativeelectrode active material layer on the current collector, the negativeelectrode active material layer comprising the carbon material accordingto any one of (L¹1) to (L¹7).

Aspects of Invention L² are as follows:

(L²1) A carbon material for a non-aqueous secondary battery, comprisinggranulated particles satisfying (1L) and (2L),

the carbon material for a non-aqueous secondary battery having anaverage dispersity D of 30 granulated particles, as determined by thefollowing measurement method, of 60% or more, the 30 particles beingrandomly selected from a cross-sectional SEM image of the carbonmaterial for a non-aqueous secondary battery.

(1L) Being made of a carbonaceous material.(2L) Satisfying the relationship |X₁−X|/X₁≦0.2, where X is avolume-based average particle diameter determined by laser diffraction,and X₁ is an equivalent circular diameter determined from across-sectional SEM image.

Measurement Method

Using a cross-sectional SEM image, grid lines are drawn to split theminor axis and the major axis of a target granulated particle each into20 parts. Using cells in the grid, the granulated particle iscompartmentalized as defined below. The expectation E of void area ofeach compartment is calculated using equation (A) below, and thedispersity D of the granulated particle is calculated using equation (B)below.

The cross-sectional SEM image is a reflected electron image acquired atan acceleration voltage of 10 kV.

Definition of Compartment of Granulated Particle

The compartment is defined as a granulated particle portion and/or aregion where a void is present in the granulated particle in each cellof the above-described grid. The outside of the boundary of thegranulated particle is excluded from the compartment.

Expectation E [μm²] of void area in target compartment=(gross area [μm²]of internal voids of one target granulated particle)/{(cross-sectionalarea [μm²] of one target granulated particle)×(area [μm²] of targetcompartment)}  Equation (A)

Dispersity D (%)=(sum total [μm²] of areas of compartments that satisfy(gross area [μm²] of voids in target compartment)/(expectation E [μm²]of void area in target compartment)=0.5 or greater)/(sum total [μm²] ofareas of all the compartments of one target granulatedparticle)×100  Equation (B)

(L²2) The carbon material for a non-aqueous secondary battery accordingto (L²1), wherein the granulated particles satisfy the relationship|R−R₁|≦0.1, where R is a roundness determined with a flow-type particleimage analyzer, and R₁ is a roundness determined from a cross-sectionalSEM image.(L²3) The carbon material for a non-aqueous secondary battery accordingto (L²1) or (L²2), wherein the carbon material has a tap density of 0.7g/cm³ or more.(L²4) The carbon material for a non-aqueous secondary battery accordingto any one of (L²1) to (L²3), wherein the carbon material has aroundness, as determined by flow-type particle image analysis, of 0.88or greater.(L²5) The carbon material for a non-aqueous secondary battery accordingto any one of (L²1) to (L²4), wherein the graphite particles arespheroidal graphite particles formed by granulation of flake graphite,crystalline graphite, and vein graphite.(L²6) The carbon material for a non-aqueous secondary battery accordingto any one of (L²1) to (L²5), wherein the granulation is carried out byapplying at least one type of mechanical energy selected from impact,compression, friction, and shear force.(L²7) The carbon material for a non-aqueous secondary battery accordingto any one of (L²1) to (L²6), wherein the granulation is carried out byplacing the graphite in an apparatus comprising a rotatable member thatrotates at a high speed in a casing and having a rotor equipped with aplurality of blades in the casing, and applying any one of impact,compression, friction, and shear force to the graphite placed in theapparatus by rotating the rotor at a high speed.(L²8) A non-aqueous secondary battery comprising:

a positive electrode and a negative electrode, each being capable ofoccluding and releasing lithium ions; and

an electrolyte,

the negative electrode comprising a current collector and a negativeelectrode active material layer on the current collector, the negativeelectrode active material layer comprising the carbon material accordingto any one of (L²1) to (L²7).

Aspects of Invention L³ are as follows:

(L³1) A carbon material for a non-aqueous secondary battery, comprisinggranulated particles satisfying (1L) and (2L),

the carbon material for a non-aqueous secondary battery having anaverage inter-void distance Z (Zave) of 30 granulated particles definedbelow and a volume-based average particle diameter X determined by laserdiffraction in a ratio (Zave/X) of 0.060 or less, the 30 particles beingrandomly selected from a cross-sectional SEM image of the carbonmaterial for a non-aqueous secondary battery.

(1L) Being made of a carbonaceous material.(2L) Satisfying the relationship |X₁−X|/X₁≦0.2, where X is avolume-based average particle diameter determined by laser diffraction,and X₁ is an equivalent circular diameter determined from across-sectional SEM image.

Definition of Average Inter-Void Distance Z (Zave) of 30 Particles

Three lines are drawn that are parallel to the minor axis of thegranulated particle and split the major axis of the granulated particleinto four parts, and inter-void distances Z (μm) of the granulatedparticle on each line are each measured. The average of 30 particles intotal is calculated. This is defined as the average Z (Zave) of 30particles.

The cross-sectional SEM image is a reflected electron image acquired at10 kV.

(L³2) The carbon material for a non-aqueous secondary battery accordingto (L³1), wherein the carbon material has a standard deviation (W) ofvoid sizes Y of 30 granulated particles defined below and a volume-basedaverage particle diameter X determined by laser diffraction in a ratio(W/X) of 0.018 or less, the 30 particles being randomly selected from across-sectional SEM image of the carbon material for a non-aqueoussecondary battery.

Definition of Standard Deviation (W) of Void Sizes Y of 30 Particles

Three lines are drawn that are parallel to the minor axis of thegranulated particle and split the major axis of the granulated particleinto four parts, and void sizes Y (μm) of the granulated particle oneach line are each measured. The standard deviation of 30 particles intotal is calculated. This is defined as the standard deviation (W) ofvoid sizes Y of 30 particles.

(L³3) The carbon material for a non-aqueous secondary battery accordingto (L³1) or (L³2), wherein 70% or more of 30 granulated particlesrandomly selected from a cross-sectional SEM image of the carbonmaterial for a non-aqueous secondary battery have slit-like voids, andthe slit-like voids are arranged mainly in layers.(L³4) The carbon material for a non-aqueous secondary battery accordingto any one of (L³1) to (L³3), wherein the carbon material has a tapdensity of 0.7 g/cm³ or more.(L³5) The carbon material for a non-aqueous secondary battery accordingto any one of (L³1) to (L³4), wherein the carbon material has aroundness, as determined by flow-type particle image analysis, of 0.88or greater.(L³6) The carbon material for a non-aqueous secondary battery accordingto any one of (L³1) to (L³5), wherein the graphite particles arespheroidal graphite particles formed by granulation of flake graphite,crystalline graphite, and vein graphite.(L³7) The carbon material for a non-aqueous secondary battery accordingto any one of (L³1) to (L³6), wherein the granulation is carried out byapplying at least one type of mechanical energy selected from impact,compression, friction, and shear force.(L³8) The carbon material for a non-aqueous secondary battery accordingto any one of (L³1) to (L³7), wherein the granulation is carried out byplacing the graphite in an apparatus comprising a rotatable member thatrotates at a high speed in a casing and having a rotor equipped with aplurality of blades in the casing, and applying any one of impact,compression, friction, and shear force to the graphite placed in theapparatus by rotating the rotor at a high speed.(L³9) A non-aqueous secondary battery comprising:

a positive electrode and a negative electrode, each being capable ofoccluding and releasing lithium ions; and

an electrolyte,

the negative electrode comprising a current collector and a negativeelectrode active material layer on the current collector, the negativeelectrode active material layer comprising the carbon material accordingto any one of (L³1) to (L³8).

Effects of the Invention

The carbon material of Invention A, when used as a negative electrodeactive material for a non-aqueous secondary battery, can provide anon-aqueous secondary battery having a high capacity and goodlow-temperature output characteristics and cycle characteristics.

The inventors believe that the above effect of the carbon materialaccording to Invention A is due to the following reason.

Specifically, the intra-particle pores of the carbon material formed tohave a moderately fine intra-particle void structure such that thecumulative pore volume at pore diameters in a range of 0.01 μm to 1 μmis 0.08 mL/g or more, and the ratio of the mode pore diameter (PD) in apore diameter range of 0.01 μm to 1 μm in a pore distribution determinedby mercury intrusion to the volume-based average particle diameter (d50)(PD/d50(%)) is 1.8 or less allow an electrolyte solution to be smoothlyand efficiently distributed into the particles. This enables effectiveand efficient use of Li-ion insertion/extraction sites in the particlesas well as on the periphery of the particles during charging anddischarging, thus providing a high capacity and good low-temperatureoutput characteristics.

The production method of Invention B, that is, the method for producinga carbon material for a non-aqueous secondary battery, comprising thestep of granulating a raw carbon material, can produce carbon materialsfor non-aqueous secondary batteries having various types of particlestructures and stably produce spheroidized graphite particles that canbe processed in bulk, have a moderately increased particle diameter(particle size), a high degree of spheroidization, good fillingproperties, and low anisotropy, and generate little amount of finepowder.

The inventors believe that the above effect is produced due to thefollowing reason.

As a result of the addition of a granulating agent, the liquid adheresbetween particles to form liquid bridges (a phenomenon where bridges arebuilt between the particles by the liquid). An attractive force causedby the capillary negative pressure in the liquid bridges and the surfacetension of the liquid acts as a liquid cross-linking adhesive forcebetween the particles to increase the liquid cross-linking adhesionbetween the raw carbon materials, allowing the raw carbon materials toadhere more firmly to each other. In addition, the granulating agentacts as a lubricant to reduce the generation of fine powder from the rawcarbon materials. Furthermore, most of the fine powder generated duringthe granulation step adhere to the raw carbon materials due to theincreased liquid cross-linking adhesive force, which leads to reducedindependent fine powder particles. These effects enable the productionof spheroidized graphite particles that include raw carbon materialsadhering more firmly to each other, have a moderately increased particlediameter and a high degree of spheroidization, and generate littleamount of fine powder.

When the granulating agent contains an organic solvent, the organicsolvent has no flash point or a flash point of 5° C. or higher. This canavoid the risk of ignition of the granulating agent induced by impact orheat during the granulation step, fire, and explosion, and thusspheroidized graphite particles can be produced stably and efficiently.

The carbon material produced by the method of the present invention hasa structure in which fine powder having a great number of Li-ioninsertion/extraction sites exists on and in the particles. Furthermore,the structure formed by the granulation of a plurality of raw carbonmaterials enables effective and efficient use of the Li-ioninsertion/extraction sites in the particles as well as on the peripheryof the particles. As a result, the use of the carbon material obtainedby the present invention in a non-aqueous secondary battery providesexcellent input-output characteristics.

The carbon material for a non-aqueous secondary battery of Invention Chas so high particle strength as to generate little amount of finepowder even upon physical impact and, when used as a negative electrodeactive material, can provide a non-aqueous secondary battery,particularly, a lithium secondary battery, having a capacity as high as355 mAh/g or more and excellent input-output characteristics andexcellent cycle characteristics.

The reason why using the carbon material of Invention C as a negativeelectrode active material can provide a non-aqueous secondary battery,particularly, a lithium ion secondary battery, having excellentinput-output characteristics and excellent cycle characteristics isprobably as follows:

When an electrode plate is formed using a carbon material as a negativeelectrode active material, step (A) of preparing a slurry by kneadingthe carbon material with a binder and other materials and step (B) ofincreasing the density by applying the slurry to a current collector,drying the slurry, and further applying a pressure, for example, with aroll press are typically employed. In step (A) of preparing a slurry, itis necessary to sufficiently knead the carbon material with a binder andother materials in order to bond the binder to the particle surface ofthe carbon material. During the kneading, the carbon materialexperiences a mechanical stress. Also in step (B) of increasing thedensity, the carbon material experiences a mechanical stress. Thesestresses can cause the carbon material, for example, to fracture togenerate fine powder. Even if the fine powder is apparently in contactwith parent particles of the carbon material after the formation of anelectrode plate, when the electrode plate is used as a negativeelectrode of a non-aqueous secondary battery, the fine powder readilyseparates from the parent particles of the carbon material duringcharging and discharging in initial conditioning. This leads to (i) anincrease in resistance between the particles due to a conductive pathbreak (reduction in electrical conductivity) or (ii) an increase inresistance due to increased side reactions (film formation) by anincreased contact area with an electrolyte solution, which presumablycauses degradation of input-output characteristics.

When a non-aqueous secondary battery is charged, ions such as lithiumions are inserted into carbon material particles, a negative electrodeactive material, to swell the particles, and when the non-aqueoussecondary battery is discharged, the ions are extracted from the carbonmaterial particles to shrink the carbon material particles. Non-aqueoussecondary batteries are rechargeable batteries, and carbon materialparticles repeatedly swell and shrink upon repeated charging anddischarging. In this swelling and shrinking of the carbon materialparticles, fine powder is separated and isolated from parent particlesof the carbon material and stops contributing to charging anddischarging, which presumably causes a reduction in battery capacity.This separated and isolated fine powder tends to increase as chargingand discharging is repeated, which presumably results in degradation incycle characteristics.

The carbon material for a non-aqueous secondary battery of Invention Csatisfies inequality (1C): Q_(5min) (%)/D50 (μm)≦3.5, where Q_(5min) (%)is a frequency (%) of particles with a diameter of 5 μm or less measuredusing a flow-type particle image analyzer after the carbon material hasbeen irradiated with ultrasonic waves of 28 kHz at a power of 60 W for 5minutes, and D50 (μm) is a volume-based median diameter determined bylaser diffraction/scattering after the carbon material has beenirradiated with ultrasonic waves of 28 kHz at a power of 60 W for 1minute. This means that the carbon material has a high particle strengthand generates little amount of fine powder when a mechanical stress,such as a physical impact, is applied. That is to say, little amount offine powder is generated in the above step (A) of preparing a slurry andstep (B) of increasing the density. Thus, using the carbon material ofthe present invention as a negative electrode active material provides anon-aqueous secondary battery (particularly, a lithium ion secondarybattery) that experiences less reduction in electrical conductivity andless increase in side reaction and has excellent input-outputcharacteristics. Furthermore, the carbon material of the presentinvention, for its high particle strength, generates little amount ofseparated and isolated fine powder upon repeated charging anddischarging and, in turn, is unlikely to experience a reduction inelectrical conductivity, thus providing a non-aqueous secondary battery(lithium ion secondary battery) having excellent cycle characteristics.

The carbon material of Invention D, when used as a negative electrodeactive material for a non-aqueous secondary battery, can provide anon-aqueous secondary battery having a high capacity and goodlow-temperature output characteristics and cycle characteristics.

The inventors believe that the above effect of the carbon materialaccording to Invention D is due to the following reason.

Specifically, the carbon material according to Invention D, as comparedwith traditional carbon materials containing carbonaceous materials onparticle surfaces, has a high tap density despite its large specificsurface area (SA) (m²/g), as determined by BET method. Thus, the carbonmaterial according to Invention D allows Li-ion insertion/extractionsites to be used over an extensive area and is excellent in fillingproperties of a negative electrode, thus providing a carbon material fora battery having good low-temperature output characteristics and a highcapacity.

The carbon material of Invention E, when used as a negative electrodeactive material for a non-aqueous secondary battery, can provide anon-aqueous secondary battery having a high capacity and goodlow-temperature output characteristics and cycle characteristics.

The inventors believe that the above effect of the carbon materialaccording to Invention E is due to the following reason.

The carbon material according to Invention E, as compared withtraditional carbon materials containing carbonaceous materials onparticle surfaces, has a large specific surface area (SA), as determinedby BET method, and thus allows Li-ion insertion/extraction sites to beused over an extensive area. Despite the large specific surface area(SA), as determined by BET method, the carbon material according toInvention E has a low true density (i.e., contains a high proportion oflow-crystallinity carbonaceous material components), and thus providesgood insertion/extraction of Li ions. That is to say, a carbon materialfor a non-aqueous secondary battery that combines an improvement ininput-output characteristics due to its specific surface area and animprovement in input-output characteristics due to its low-crystallinitycarbonaceous material can be provided.

The composite carbon material of Invention F, when used as a negativeelectrode active material for a non-aqueous secondary battery, canprovide a non-aqueous secondary battery having a high capacity and goodlow-temperature output characteristics and cycle characteristics.

The inventors believe that the above effect of the composite carbonmaterial according to Invention F is due to the following reason.

Specifically, the average value of microscopic Raman R values of 30randomly selected composite carbon materials of 0.1 to 0.85 and thestandard deviation (σ_(R)) of 0.1 or less means that the compositecarbon material uniformly contains, on the surface of the carbonmaterial (A), a low-crystallinity carbonaceous material into and fromwhich Li ions are readily inserted and extracted. This inhibits aconcentrated excessive current flow into a specific site on the carbonmaterial (A) into and from which Li ions are readily inserted andextracted and enables uniform and smooth insertion/extraction of Li ionseven at low temperatures and during high-current charging anddischarging, thus providing a high capacity and excellentlow-temperature output characteristics and cycle characteristics.

The carbon material of Invention G, when used as a negative electrodeactive material for a non-aqueous secondary battery, can provide anon-aqueous secondary battery having a capacity as high as 355 mAh/g ormore and excellent low-temperature output characteristics.

The inventors believe that the above effect of the carbon materialaccording to Invention G is due to the following reason.

The investigation by the present inventors has shown that the cumulativepore volume at pore diameters in a range of 2 to 4 nm larger than aspecific value increases the number of lithium-ion insertion/extractionsites on the carbon material, which promotes the lithiuminsertion/extraction reaction on the carbon material surface duringcharging and discharging to improve low-temperature outputcharacteristics. In addition, the tap density of 0.83 g/cm³ or moresmoothens the movement of electrolyte solution between particles toimprove input-output characteristics.

The carbon material of Invention H, when used as a negative electrodeactive material for a non-aqueous secondary battery, can provide anon-aqueous secondary battery having a high capacity and goodlow-temperature output characteristics and cycle characteristics.

The inventors believe that the above effect of the carbon materialaccording to Invention H is due to the following reason.

Specifically, having a Raman R value in the above range means that thecarbon material has a moderately disordered surface crystal structureand a sufficient number of Li-ion insertion/extraction sites. Having athermal weight loss ratio per unit area (ΔTG/SA) in the above rangemeans that the number of labile carbons, which are carbons prone tothermal oxidation, is moderately small. This enables Li ions to smoothlymove without being impeded during charging and discharging. Thus,despite the moderately disordered surface crystal structure, themoderately small number of labile carbons, which are carbons prone tothermal oxidation, enables Li ions to smoothly move without beingimpeded during charging and discharging despite the sufficient number ofLi-ion insertion/extraction sites, thus providing a high capacity andgood low-temperature output characteristics.

The carbon material of Invention I, when used as a negative electrodeactive material for a non-aqueous secondary battery, can provide anon-aqueous secondary battery having a high capacity and goodlow-temperature output characteristics and cycle characteristics.

The inventors believe that the above effect of the carbon materialaccording to Invention I is due to the following reason.

Specifically, having Y_(i) (oxygen functional group dispersity given bythe above equation (2I)) and X_(i) (volume-based average particlediameter (d50) (μm)) in the above ranges means that oxygen functionalgroups are not maldistributed on the particle surface and dispersed alsoin the particles. The presence of oxygen functional groups at graphitecrystal edge portions that functions as Li-ion insertion/extractionsites suggests that the carbon material of Invention I has a moderatenumber of Li-ion insertion/extraction sites not only on but also in theparticles. This enables efficient Li-ion insertion/extraction also inthe particles, thus providing a high capacity and good low-temperatureoutput characteristics.

The production method of Invention J can provide composite particles fora non-aqueous secondary battery, comprising spheroidally granulatedgraphite particles having a structure in which fine powder having agreat number of Li-ion insertion/extraction sites exists on and in theparticles, the graphite particles being uniformly coated with acarbonaceous material. The composite particles, when used as a negativeelectrode active material for a non-aqueous secondary battery, canprovide a non-aqueous secondary battery having a high capacity andexcellent low-temperature output characteristics and high-temperaturestorage characteristics.

The inventors believe that the above effect of the production methodaccording to Invention J is due to the following reason.

As a result of the addition of a granulating agent, the liquid adheresbetween particles to form liquid bridges (a phenomenon where bridges arebuilt between the particles by the liquid). An attractive force causedby the capillary negative pressure in the liquid bridges and the surfacetension of the liquid acts as a liquid cross-linking adhesive forcebetween the particles to increase the liquid cross-linking adhesionbetween the raw carbon materials (hereinafter also referred to as rawgraphites), allowing the raw graphites to adhere more firmly to eachother. In addition, the granulating agent acts as a lubricant to reducethe generation of fine powder from the raw graphites. Furthermore, mostof the fine powder generated during the granulation step adhere to theraw graphites due to the increased liquid cross-linking adhesive force,which leads to reduced independent fine powder particles. These effectsenable the production of spheroidized graphite particles that includeraw graphite adhering more firmly to each other, have a moderatelyincreased particle diameter and a high degree of spheroidization, andgenerate little amount of fine powder.

The composite particles produced by the method of Invention J has astructure in which fine powder having a great number of Li-ioninsertion/extraction sites exists on and in the particles. Furthermore,the structure formed by the granulation of a plurality of raw graphitesenables effective and efficient use of the Li-ion insertion/extractionsites in the particles as well as on the periphery of the particles.

Furthermore, in mixing the resulting granulated graphite particles withan organic compound, serving as a carbonaceous material precursor, andheat-treating the resulting mixture to obtain composite particlescontaining graphite particles and a carbonaceous material, selecting anorganic compound, serving as a carbonaceous material precursor, and agranulating agent having a good affinity with each other allows theorganic compound, serving as a carbonaceous material precursor, to beuniformly deposited on the surface of the granulated graphite. Thisenables the carbonaceous material suitable for Li-ioninsertion/extraction to uniformly cover the composite particle surfaceto prevent the exposure of the granulated graphite surface.

As a result, the composite particles obtained by Invention J, when usedfor a non-aqueous secondary battery, can provide a high capacity andexcellent input-output characteristics and high-temperature storagecharacteristics.

The carbon material of Invention K, when used as a negative electrodeactive material for a non-aqueous secondary battery, can provide anon-aqueous secondary battery having a high capacity and goodlow-temperature output characteristics and cycle characteristics.

The inventors believe that the above effect of the carbon materialaccording to Invention K is presumably due to the following reason.

True density is an indicator of crystallinity of carbon materials. Asthe true density of a carbon material decreases and gets away from itstheoretical value, the crystallinity lowers, and thus the particles ofthe carbon material will probably get harder, resulting in low fillingproperties under a specific load.

The density under a specific load minus a tap density will probably bean indicator that reflects the surface slidability and the particlestrength of a carbon material under a specific load.

Specifically, having a true density and a density under a specific loadminus a tap density in a specific relationship means that the carbonmaterial of Invention K, as compared with traditional carbon materialshaving comparable crystallinities, undergoes less particle fracture andis easier to fill, leading to reduced particle fracture in pressing anelectrode. This reduces the separation of amorphous carbon covering atleast part of the carbon material during the pressing and enablesfilling to a predetermined density while maintaining lithiuminsertion/extraction sites derived from amorphous carbon and theparticle shape, thus providing a high capacity and good low-temperatureoutput characteristics.

The carbon material of Inventions L, when used as a negative electrodeactive material for a non-aqueous secondary battery, can provide anon-aqueous secondary battery having a high capacity and goodlow-temperature output characteristics and cycle characteristics.

The inventors believe that the above effects of the carbon materialsaccording to Inventions L (L¹ to L³) are presumably due to the followingreason.

Specifically, fining intra-particle pores (L¹), uniformly dispersingintra-particle pores (L²), or controlling the orientation of and theinterval between intra-particle voids (L³) allows an electrolytesolution to be smoothly and efficiently distributed into the particles.This enables effective and efficient use of Li-ion insertion/extractionsites in the particles as well as on the periphery of the particlesduring charging and discharging, thus providing a high capacity and goodlow-temperature output characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the relationship between X_(d) and 10Y_(d) offourth Examples and Comparative Examples. Points of (X_(d), 10Y_(d)):Example D1, (7.38, 1.16); Example D2, (5.79, 1.19); Example D3, (5.15,1.18); Example D4, (4.30, 1.20); Example D5, (2.88, 1.19); ComparativeExample D1, (3.92, 1.08); Comparative Example D2, (2.97, 1.11);Comparative Example D3, (3.53, 1.11); Comparative Example D4, (2.51,1.15); Comparative Example D5, (4.48, 1.07); Comparative Example D6,(1.82, 1.21);

FIG. 2 is a graph showing the relationship between X_(e) and Y_(e) offifth Examples and Comparative Examples. Points of (X_(e), Y_(e)):Example E1, (7.38, 2.25); Example E2, (5.79, 2.24); Example E3, (5.15,2.24); Example E4, (4.30, 2.23); Example E5, (2.88, 2.22); Example E6,(8.69, 2.23); Example E7, (6.21, 2.22); Comparative Example E1, (3.92,2.25); Comparative Example E2, (2.97, 2.24); Comparative Example E3,(3.53, 2.25); Comparative Example E4, (2.51, 2.24); Comparative ExampleE5, (4.48, 2.25); Comparative Example E6, (1.82, 2.23);

FIG. 3 is a graph showing the relationship between X_(i) and Y_(i) ofninth Examples and Comparative Examples. Points of (X_(i), Y_(i)):Example I1, (12.7, 0.108); Example I2, (12.9, 0.071); Example I3, (16.3,0.063); Example I4, (19.4, 0.047); Comparative Example I1, (10.9,0.066); Comparative Example I2, (11.3, 0.060); Comparative Example I3,(15.4, 0.053); Comparative Example I4, (18.2, 0.047);

FIG. 4 is a graph showing the relationship between high-temperaturestorage characteristics and low-temperature output characteristics oftenth Examples and Comparative Examples. Points of (high-temperaturestorage characteristics, low-temperature output characteristics):Example J1, (98.9, 109.9); Example J2, (100.4, 104.8); Example J3,(101.1, 103.1); Reference Example J1, (98.6, 94.4); Reference ExampleJ2, (100.0, 100.0); Reference Example J3, (100.4, 91.2); ComparativeExample J1, (104.4, 68.1);

FIG. 5 is a graph showing the relationship between inequality (1K) andtrue density of eleventh Examples and Comparative Examples. The resultsof Example K1 to 6 and Comparative Example K1 to K8 are shown with theright side of inequality (1K) plotted on the vertical axis and the truedensity of a carbon material on the horizontal axis;

FIG. 6 is a graph showing the relationship between inequality (3K) andtrue density of eleventh Examples and Comparative Examples. The resultsof Example K1 to 6 and Comparative Example K1 to K8 are shown with theright side of inequality (3K) plotted on the vertical axis and the truedensity of a carbon material on the horizontal axis;

FIG. 7 shows binarized images (photographs substituted for drawings) ofone granulated particle in the carbon material of Example L1 and alogarithmic graph, as determined by the box-counting method, with boxsize plotted on the horizontal axis and the number of boxes counted onthe vertical axis;

FIG. 8 shows binarized images (photographs substituted for drawings) ofone granulated particle in the carbon material of Comparative Example L1and a logarithmic graph, as determined by the box-counting method, withbox size plotted on the horizontal axis and the number of boxes countedon the vertical axis;

FIG. 9 shows a cross-sectional SEM image (a photograph substituted for adrawing) and a binarized image of one granulated particle in the carbonmaterial of Example L1;

FIG. 10 shows exemplary images (photographs substituted for drawings)unsuitable for analysis in SEM image binarization;

FIG. 11 shows a method of binarization, drawing of grid lines, andcompartmentalization of one granulated particle in the carbon materialof Example L1 (photographs substituted for drawings);

FIG. 12 shows a compartment and a non-compartment in a cell defined bygrid lines (photographs substituted for drawings);

FIG. 13 shows a method for calculating the void distance and thedistance between voids of one granulated particle in the carbon materialof Example L1 (photographs substituted for drawings);

FIG. 14 is an SEM image of one granulated particle in the carbonmaterial of Example L1 (a photograph substituted for a drawing); and

FIG. 15 is an SEM image of one granulated particle in the carbonmaterial of Comparative Example L1 (a photograph substituted for adrawing).

MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described in detail. It should beappreciated that the following description of the features of theinvention is one aspect (a typical example) of the present invention,and other variations may be applied without departing from the spirit ofthe invention.

One embodiment of the carbon material for a non-aqueous secondarybattery according to the present invention is a carbon material for anon-aqueous secondary battery, comprising a graphite capable ofoccluding and releasing lithium ions, the carbon material having acumulative pore volume at pore diameters in a range of 0.01 μm to 1 μmof 0.08 mL/g or more, a roundness, as determined by flow-type particleimage analysis, of 0.88 or greater, and a pore diameter to particlediameter ratio (PD/d50(%)) of 1.8 or less, the ratio being given byequation (1A):

PD/d50(%)=mode pore diameter (PD) in a pore diameter range of 0.01 μm to1 μm in a pore distribution determined by mercury intrusion/volume-basedaverage particle diameter (d50)×100  (1A).

Another embodiment is a carbon material for a non-aqueous secondarybattery capable of occluding and releasing lithium ions, the carbonmaterial being formed from a plurality of graphite particles withoutbeing pressed and having a pore diameter to particle diameter ratio(PD/d50(%)) of 1.8 or less, the ratio being given by equation (1A):

PD/d50(%)=mode pore diameter (PD) in a range of 0.01 μm to 1 μm in apore distribution determined by mercury intrusion/volume-based averageparticle diameter (d50)×100  (1A).

“Without being pressed” means not being pressed to the extent that thedensity or the isotropy of the graphite particles is increased.Specifically, for example, the pressure may be 50 kgf/cm² or more, 100kgf/cm² or more, or 200 kgf/cm² or more.

Types of Carbon Material for Non-Aqueous Secondary Battery

Examples of the carbon material for a non-aqueous secondary batterycapable of occluding and releasing lithium ions according to the presentinvention include, but are not limited to, graphites, amorphous carbons,and carbonaceous materials with low degrees of graphitization. Of these,graphites are preferred because it is commercially readily available,has, theoretically, a charge-discharge capacity as high as 372 mAh/g,and, further, is more effective in improving high-current-densitycharge-discharge characteristics as compared with other negativeelectrode active materials. Graphites having low impurity contents arepreferred, and, if necessary, various known purification treatments maybe carried out before use. Examples of graphites include naturalgraphites and artificial graphites, and natural graphites, which havehigh capacities and good high-current-density charge-dischargecharacteristics, are more preferred.

These may be coated with a carbonaceous material, for example, anamorphous carbon or a graphitized carbon. In the present invention,these graphites may be used alone or in combination.

Examples of amorphous carbons include particles obtained by burning abulk mesophase and particles obtained by infusibilizing and burning acarbon precursor.

Examples of carbonaceous material particles with low degrees ofgraphitization include those obtained by burning organic substancestypically at a temperature lower than 2,500° C. Examples of organicsubstances include coal-derived heavy oils, such as coal-tar pitch anddry distillation/liquefaction oil; straight-run heavy oils, such asatmospheric residues and vacuum residues; petroleum-derived heavy oilssuch as heavy oils resulting from cracking, such as ethylene tarproduced as a by-product of thermal cracking of crude oil, naphtha, orother oils; aromatic hydrocarbons, such as acenaphthylene, decacyclene,and anthracene; nitrogen-containing cyclic compounds, such as phenazineand acridine; sulfur-containing cyclic compounds, such as thiophene;aliphatic cyclic compounds, such as adamantane; and thermoplasticpolymers, including polyphenylenes, such as biphenyl and terphenyl,polyvinyl esters, such as polyvinyl chloride, polyvinyl acetate, andpolyvinyl butyral, and polyvinyl alcohols.

Depending on the degree of graphitization of the carbonaceous materialparticles, the burning temperature may be 600° C. or higher, preferably900° C. or higher, more preferably 950° C. or higher, and may betypically in the range of lower than 2,500° C., preferably 2,000° C. orlower, more preferably 1,400° C. or lower.

In burning, the organic substance may be mixed with acids, such asphosphoric acid, boric acid, and hydrochloric acid, and alkalis, such assodium hydroxide.

Examples of artificial graphites include those obtained by burning andgraphitizing organic substances such as coal-tar pitch, coal-derivedheavy oils, atmospheric residues, petroleum-derived heavy oils, aromatichydrocarbons, nitrogen-containing cyclic compounds, sulfur-containingcyclic compounds, polyphenylenes, polyvinyl chlorides, polyvinylalcohols, polyacrylonitriles, polyvinyl butyrals, natural polymers,polyphenylene sulfides, polyphenylene oxides, furfuryl alcohol resins,phenol-formaldehyde resins, and imide resins.

The burning temperature may be in the range of 2,500° C. to 3,200° C.,and in burning, a silicon-containing compound, a boron-containingcompound, or other compounds may be used as a graphitizing catalyst.

Natural graphites are classified into flake graphite, crystallinegraphite, vein graphite, and amorphous graphite depending on theirproperties (see “Encyclopedia of powder process industry and technology”(Industrial Technology Center, 1974), Section “Graphite”, and “HANDBOOKOF CARBON, GRAPHITE, DIAMOND AND FULLERENES” (published byNoyesPubLications)). Crystalline graphite and vein graphite have highestdegrees of graphitization of 100%, and flake graphite has a next highestdegree of graphitization of 99.9%. Graphites having higher degrees ofgraphitization are more suitable for the present invention. Inparticular, those having low impurity contents are preferred, and, ifnecessary, various known purification treatments may be carried outbefore use.

Natural graphites are produced in Madagascar, China, Brazil, Ukraine,Canada, and other districts. Among natural graphites, crystallinegraphite is mainly produced in Sri Lanka, and amorphous graphite ismainly produced in the Korean Peninsula, China, Mexico, and otherdistricts.

Among natural graphites, for example, crystalline, flake, and veinnatural graphites, highly purified flake graphite, and natural graphitesubjected to spheroidization described below (hereinafter referred to asspheroidized natural graphite) are preferred. Of these, in an embodimentof the present invention, spheroidized natural graphite is mostpreferred because it can form favorable fine pores in a carbon materialto provide excellent particle-filling properties and charge-dischargeload characteristics.

For carbon materials for non-aqueous secondary batteries, use may alsobe made of natural graphite or artificial graphite particles coated withan amorphous carbon and/or a graphite material having a low degree ofgraphitization. In addition, oxides and other metals may be contained.Examples of other metals include metals capable of forming alloys withLi, such as Sn, Si, Al, and Bi.

Method for Producing Carbon Material for Non-Aqueous Secondary Battery

In one embodiment, the carbon material of the present invention can beproduced, for example, by spheroidizing a flake natural graphite whoseparticle size has been adjusted to a d50 of 80 μm or less whiledepositing and/or incorporating fine powder generated during thespheroidization (granulation) on and/or into a base material, thegraphite that has been subjected to spheroidization (hereinafter alsoreferred to as spheroidized graphite). Specifically, the carbon materialis preferably produced by a method for producing a carbon material for anon-aqueous secondary battery, comprising a granulation step ofgranulating a raw carbon material by applying at least one type ofmechanical energy selected from impact, compression, friction, and shearforce, the granulation step being carried out in the presence of agranulating agent that satisfies conditions 1) and 2):

1) being liquid during the step of granulating the raw carbon material;and

2) in the granulating agent, no organic solvent is contained, or ifcontained, at least one of the organic solvents has no flash point or aflash point of 5° C. or higher.

In another embodiment, the carbon material of the present invention canbe produced by a method for producing composite particles for anon-aqueous secondary battery comprising a granulated carbon materialand a carbonaceous material having lower crystallinity than thegranulated carbon material, the method comprising the steps of 1) and2):

1) applying at least one type of mechanical energy selected from impact,compression, friction, and shear force in the presence of a granulatingagent having an aniline point of 80° C. or lower or no aniline point togranulate a raw carbon material; and

2) mixing the granulated carbon material obtained in 1) with an organiccompound, serving as a carbonaceous material precursor, andheat-treating the mixture.

As long as the granulation step is included, the method may optionallyinclude other steps. The other steps may be carried out individually orsimultaneously. One embodiment includes the following 1st step to 6thstep.

1st step: adjusting the particle size of a raw carbon material

2nd step: mixing the raw carbon material with a granulating agent

3rd step: granulating the raw carbon material

4th step: removing the granulating agent

5th step: increasing the purity of the granulated carbon material

5′th step: increasing the crystallinity of the granulated carbonmaterial

6th step: depositing a carbonaceous material having lower crystallinitythan the raw carbon material on the granulated carbon material

These steps will be described below.

1st Step: Adjusting Particle Size of Raw Carbon Material

In the present invention, any raw carbon material may be used, andartificial graphites and natural graphites described above can be used.In particular, natural graphites, which have high crystallinity and highcapacities, are suitable for use.

Examples of natural graphites include crystalline, flake, vein, andplate-like natural graphites, among which flake graphite is preferred.

The raw carbon material such as a flake graphite obtained through the1st step, which is used as a raw material of a spheroidized graphite,has an average particle diameter (volume-based median diameter: d50) ofpreferably 1 μm or more, more preferably 2 μm or more, still morepreferably 3 μm or more, preferably 80 μm or less, more preferably 50 μmor less, still more preferably 35 μm or less, very preferably 20 μm orless, particularly preferably 10 μm or less, most preferably 8 μm orless. The average particle diameter can be determined by the methoddescribed below.

An average particle diameter in this range can prevent the increase inirreversible capacity and the degradation of cycle characteristics andstrictly control the intra-particle void structure of the spheroidizedgraphite. This allows an electrolyte solution to be efficientlydistributed into intra-particle voids and enables the efficient use ofLi-ion insertion/extraction sites in the particles, as a result of whichlow-temperature output characteristics and cycle characteristics tend toimprove. Furthermore, such an average particle diameter can adjust theroundness of the spheroidized graphite to be high and thus allows anelectrolyte solution to smoothly move in intra-particle voids with noincrease in flection of Li-ion diffusivity, leading to improved fastcharge-discharge characteristics.

Furthermore, an average particle diameter in the above range enablesperforming granulation while depositing or incorporating the fine powdergenerated during the granulation step on or into a base material, thegranulated graphite (hereinafter referred to as granulated carbonmaterial), thus providing a granulated carbon material that has a highdegree of spheroidization and generates little amount of fine powder.

The average particle diameter (d50) of the raw carbon material can beadjusted to be in the above range, for example, by crushing and/orclassifying (natural) graphite particles.

Examples of apparatuses for use in crushing include, but are not limitedto, coarse crushers, such as shear mills, jaw crushers, impact crushers,and cone crushers; intermediate crushers, such as roll crushers andhammer mills; and fine crushers, such as mechanical crushers, air-flowcrushers, and swirl-flow crushers. Specific examples include ball mills,vibration mills, pin mills, agitation mills, jet mills, cyclone mills,and turbo mills. In particular, when graphite particles of 10 μm or lessare produced, air-flow crushers and swirl-flow crushers are suitable foruse.

In classification, any apparatuses can be used. In the case of drysieving, a rotary sieve, a shaking sieve, a gyratory sieve, a vibratorysieve, or other sieves can be used. In the case of dry air-flowclassification, a gravity classifier, an inertia classifier, or acentrifugal classifier (e.g., a classifier or a cyclone) can be used. Inthe case of wet sieving, a mechanical wet classifier, a hydraulicclassifier, a sedimentation classifier, a centrifugal wet classifier, orother classifiers can be used.

The raw carbon material obtained through the 1st step preferably hasphysical properties as described below.

The ash content of the raw carbon material is preferably 1% by mass orless, more preferably 0.5% by mass or less, still more preferably 0.1%by mass or less, based on the total mass of the raw carbon material. Theash content is preferably at least 1 ppm.

An ash content in this range can provide a non-aqueous secondary batterythat undergoes only negligible degradation of battery performance due tothe reaction between carbon material and electrolyte solution duringcharging and discharging. In addition, such an ash content does notrequire much time or energy to produce a carbon material and eliminatesthe need for equipment for preventing contamination, thus reducing theincrease in cost.

The raw carbon material has an aspect ratio of preferably 3 or greater,more preferably 5 or greater, still more preferably 10 or greater,particularly preferably 15 or greater, and preferably 1,000 or less,more preferably 500 or less, still more preferably 100 or less,particularly preferably 50 or less. The aspect ratio is determined bythe method described below. An aspect ratio in this range is less likelyto yield large particles having a particle diameter of approximately 100μm and, on the other hand, more likely to yield a robust granulatedcarbon material because a moderate contact area is provided whenpressure is applied from one direction. An excessively high aspect ratiotends to yield large particles having a particle diameter ofapproximately 100 μm. Excessively small particles tend to fail to formrobust granulated particles because a small contact area is providedwhen pressure is applied from one direction, and if the particles aregranulated, the granulated particles tend to have a specific surfacearea of more than 30 m²/g reflecting the small specific surface area offlake graphite.

For an interplanar spacing of the (002) plane (d₀₀₂) and a crystallitesize (Lc), as determined by wide-angle X-ray diffractometry, of the rawcarbon material, typically, (d₀₀₂) is 3.37 angstroms or less, and (Lc)is 900 angstroms or more; preferably, (d₀₀₂) is 3.36 angstroms or less,and (Lc) is 950 angstroms or more. The interplanar spacing (d₀₀₂) andthe crystallite size (Lc) are indicators of the crystallinity of acarbon material bulk. As the interplanar spacing of the (002) plane(d₀₀₂) decreases and the crystallite size (Lc) increases, thecrystallinity of the carbon material increases, and the amount oflithium that enters between graphite layers comes closer to thetheoretical value to increase the capacity. When the crystallinity islow, excellent battery characteristics (a high capacity and a lowirreversible capacity) that are exhibited when a high-crystallinitygraphite is used as an electrode are not exhibited. Particularlypreferably, the interplanar spacing (d₀₀₂) and the crystallite size (Lc)are both in the above ranges.

The X-ray diffraction is carried out as follows: using a mixture ofcarbon powder and X-ray standard high-purity silicon powder in an amountof about 15% by mass based on the total mass as a sample and a CuKαradiation monochromatized with a graphite monochromator as a radiationsource, a wide-angle X-ray diffractometry curve is obtained byreflection diffractometry. After that, the method of the Japan Societyfor Promotion of Scientific Research is used to determine an interplanarspacing (d₀₀₂) and a crystallite size (Lc).

The packed structure of the raw carbon material varies depending on thesize and shape of particles, the degree of interactivity betweenparticles, and other factors, and in this specification, tap density canbe used as an indicator for quantitatively discussing the packedstructure. The investigation by the present inventors has revealed thatin the case of lead particles having substantially the same true densityand average particle diameter, the tap density increases as the shapecomes closer to spheroidal and the particle surface becomes flat. Inother words, to increase the tap density, it is important that theparticle shape be rounded and closer to spheroidal, and the particlesurface be made free from frays and chips and kept flat. A particleshape closer to spheroidal and a flat particle surface significantlyimproves powder filling properties. The tap density of the raw carbonmaterial is preferably 0.1 g/cm³ or more, more preferably 0.15 g/cm³ ormore, still more preferably 0.2 g/cm³ or more, particularly preferably0.3 g/cm³ or more. The tap density is determined by the method describedbelow in Examples.

The argon-ion laser Raman spectrum of the raw carbon material is used asan indicator of conditions of a particle surface. The Raman R value, aratio of peak intensity near 1,360 cm⁻¹ to peak intensity near 1,580cm⁻¹ in the argon-ion laser Raman spectrum of the raw carbon material,is preferably 0.05 to 0.9, more preferably 0.05 to 0.7, still morepreferably 0.05 to 0.5. The Raman R value is an indicator of thecrystallinity near the surface (from the particle surface to a depth ofabout 100 angstroms) of a carbon particle, and smaller Raman R valuesindicate higher crystallinities or less disordered crystalline states.The Raman spectrum is measured by the method described below.Specifically, a sample is loaded by gravity-dropping target particlesinto a measuring cell of a Raman spectroscope, and the measuring cell isirradiated with an argon-ion laser beam while being rotated in a planeperpendicular to the laser beam. The wavelength of the argon-ion laserbeam is 514.5 nm.

The wide-angle X-ray diffractometry of the raw carbon material is usedas an indicator of the crystallinity of the whole particle. The 3R/2Hratio of intensity 3R (101) of the (101) plane based on a rhombohedralcrystal structure to intensity 2H (101) of the (101) plane based on ahexagonal crystal structure, as determined by wide-angle X-raydiffractometry, of the flake graphite is preferably 0.1 or greater, morepreferably 0.15 or greater, still more preferably 0.2 or greater. Therhombohedral crystal structure is a crystal form in which networkstructures of a graphite are stacked on top of each other at every threelayers. The hexagonal crystal structure is a crystal form in whichnetwork structures of a graphite are stacked on top of each other atevery two layers. A flake graphite having a crystal form containing ahigh proportion of rhombohedral crystal structures 3R has high Li-ionreceiving properties as compared with a graphite containing a lowproportion of rhombohedral crystal structures 3R.

The raw carbon material has a specific surface area as measured by BETmethod of preferably 0.3 m²/g or more, more preferably 0.5 m²/g or more,still more preferably 1 m²/g or more, particularly preferably 2 m²/g ormore, most preferably 5 m²/g or more, and preferably 30 m²/g or less,more preferably 20 m²/g or less, still more preferably 15 m²/g or less.The specific surface area as measured by BET method is determined by themethod in Examples below. A specific surface area of the raw carbonmaterial in this range improves the Li-ion receiving properties, whichcan prevent the decrease in battery capacity due to the increase inirreversible capacity. An excessively small specific surface area of theflake graphite reduces the Li-ion receiving properties, and anexcessively large specific surface area tends to fail to prevent thedecrease in battery capacity due to the increase in irreversiblecapacity.

The water content of the raw carbon material (raw graphite) of agranulated carbon material is preferably 1% by mass or less, morepreferably 0.5% by mass or less, still more preferably 0.1% by mass orless, particularly preferably 0.05% by mass or less, most preferably0.01% by mass or less, based on the total mass of the raw graphite. Thewater content is preferably at least 1 ppm. The water content can bedetermined, for example, by a method in accordance with JIS M8811. Awater content in this range advantageously increases the interparticleelectrostatic attraction during spheroidization, leading to increasedinterparticle adhesion, which facilitates the deposition of fine powderon a base material and the incorporation of fine powder intospheroidized particles. In addition, such a water content can preventthe decrease in wettability when a hydrophobic granulating agent isused.

To adjust the water content of the raw carbon material (raw graphite) ofa granulated carbon material to be in the above range, a dryingtreatment may optionally be performed. The drying treatment is carriedout typically at 60° C. or higher, preferably 100° C. or higher, morepreferably 200° C. or higher, still more preferably 250° C. or higher,particularly preferably 300° C. or higher, most preferably 350° C. orhigher, and typically 1,500° C. or lower, preferably 1,000° C. or lower,more preferably 800° C. or lower, still more preferably 600° C. orlower. An excessively low temperature tends to fail to sufficientlyreduce the water content, and an excessively high temperature tends tolead to reduced productivity and increased cost.

The drying treatment is carried out typically for 0.5 to 48 hours,preferably 1 to 40 hours, more preferably 2 to 30 hours, still morepreferably 3 to 24 hours. An excessively long time tends to lead toreduced productivity, and an excessively short time tends to fail tofully exert a heat treatment effect.

The atmosphere in the heat treatment may be an active atmosphere, suchas an air atmosphere, or an inert atmosphere, such as a nitrogenatmosphere or an argon atmosphere. When the heat treatment is carriedout at 200° C. to 300° C., there is no particular restriction, but whenthe heat treatment is carried out at 300° C. or higher, it is preferableto use an inert atmosphere, such as a nitrogen atmosphere or an argonatmosphere, to prevent the oxidation of the graphite surface.

The surface functional group amount O/C value (%), as determined by XPS,of the flake graphite, a raw carbon material which is used as a rawmaterial of a spheroidized graphite, is preferably 0.01 or greater, morepreferably 0.1 or greater, still more preferably 0.3 or greater,particularly preferably 0.5 or greater, preferably 5 or less, morepreferably 3 or less, still more preferably 2.5 or less, particularlypreferably 2 or less, most preferably 1.5 or less. An O/C value in thisrange advantageously reduces hygroscopicity, making it easy to keep theparticles dry, and increases the interparticle electrostatic attractionduring spheroidization, leading to increased interparticle adhesion,which facilitates the deposition of fine powder on a base material andthe incorporation of fine powder into spheroidized particles.

2nd Step: Mixing Raw Carbon Material with Granulating Agent

The granulating agent for use in one embodiment of the present inventionsatisfies conditions 1) being liquid during the step of granulating theraw carbon material, and 2) in the granulating agent, no organic solventis contained, or if contained, at least one of the organic solvents hasno flash point or a flash point of 5° C. or higher.

In the subsequent 3rd step of granulating the raw carbon material, thegranulating agent satisfying these conditions forms liquid bridgesbetween the raw carbon materials, whereby an attractive force caused bythe capillary negative pressure in the liquid bridges and the surfacetension of the liquid acts as a liquid cross-linking adhesive forcebetween the particles to increase the liquid cross-linking adhesionbetween the raw carbon materials, allowing the raw carbon materials toadhere more firmly to each other.

In one embodiment of the present invention, the strength of the liquidcross-linking adhesive force between the raw carbon materials producedby the liquid bridges of the granulating agent between the raw carbonmaterials is proportional to γ cos θ value (where γ is a surface tensionof a liquid, and θ is a contact angle between the liquid and aparticle). That is to say, in granulating the raw carbon material, thegranulating agent preferably has higher wettability to the raw carbonmaterial. Specifically, it is preferable to select a granulating agentthat satisfies cos θ>0 so that γ cos θ>0 is satisfied, and thegranulating agent preferably has a contact angle θ with a graphite, asmeasured by the following method, of less than 90°.

Method for Measuring Contact Angle θ with Graphite

Onto a surface of HOPG, 1.2 μL of a granulating agent is added dropwise,and when wetting and spreading has settled down and a rate of change incontact angle θ in one second has reached 3% or lower (also referred toas a steady state), the contact angle is measured using a contact anglemeter (e.g., DM-501 automatic contact angle meter available from KyowaInterface Science Co., Ltd). When a granulating agent having a viscosityat 25° C. of 500 cP or lower is used, a value at 25° C. is employed as ameasurement of the contact angle θ, and when a granulating agent havinga viscosity at 25° C. of higher than 500 cP is used, a value at anincreased temperature where the viscosity is not higher than 500 cP isemployed.

Furthermore, as the contact angle θ between the raw carbon material andthe granulating agent comes closer to 0°, the γ cos θ value increases toincrease the liquid cross-linking adhesion between the graphiteparticles, allowing the graphite particles to adhere more firmly to eachother. Thus, the contact angle θ between the granulating agent and thegraphite is more preferably 85° or less, still more preferably 80° orless, even more preferably 50° or less, particularly preferably 30° orless, most preferably 20° or less.

Also by using a granulating agent having a high surface tension γ, the γcos θ value is increased to improve the adhesion between the graphiteparticles, and thus γ is preferably 0 or greater, more preferably 15 orgreater, still more preferably 30 or greater.

The surface tension γ of the granulating agent for use in the presentinvention is measured by the Wilhelmy method using a surface tensiometer(e.g., DCA-700 available from Kyowa Interface Science Co., Ltd).

A viscous force acts as a resistant to the extension of liquid bridgesassociated with the movement of particles, and the strength of theviscous force is proportional to viscosity. Thus, the viscosity of thegranulating agent, although not limited to any particular value as longas the granulating agent is liquid during the granulation step ofgranulating the raw carbon material, is preferably 1 cP or more duringthe granulation step.

In addition, the granulating agent has a viscosity at 25° C. ofpreferably 1 cP to 100,000 cP, more preferably 5 cP to 10,000 cP, stillmore preferably 10 cP to 8,000 cP, particularly preferably 50 cP to6,000 cP. A viscosity in this range can prevent deposited particles frombeing detached by impact force, such as a collision with a rotor or acasing, in granulating the raw carbon material.

The viscosity of the granulating agent for use in the present inventionis measured using a rheometer (e.g., ARES available from RheometricScientific) by placing an appropriate amount of a target (in this case,the granulating agent) into a cup and adjusting the temperature to apredetermined temperature. In this specification, the viscosity isdefined as a measurement at a shear rate 100 s⁻¹, in the case where theshear stress at a shear rate 100 s⁻¹ is not less than 0.1 Pa; ameasurement at 1,000 s⁻¹, in the case where the shear stress at a shearrate 100 s⁻¹ is less than 0.1 Pa; and a measurement at a shear rate atwhich the shear stress is not less than 0.1 Pa, in the case where theshear stress at a shear rate 1,000 s⁻¹ is less than 0.1 Pa. The shearstress can be not less than 0.1 Pa also by using a spindle having ashape suitable for low-viscosity fluids.

Furthermore, in the granulating agent for use in one embodiment of thepresent invention, no organic solvent is contained, or if contained, atleast one of the organic solvents has no flash point or a flash point of5° C. or higher. This can avoid the risk of ignition of the organiccompound induced by impact or heat, fire, and explosion in thesubsequent 3rd step of granulating the raw carbon material, thusachieving stable and efficient production.

In one aspect of another embodiment of the present invention (e.g., butnot limited to, Invention J), the granulating agent for use in this stepis preferably a granulating agent having an aniline point of 80° C. orlower or no aniline point.

Granulating Agent Having Aniline Point of 80° C. or Lower or No AnilinePoint

Since the solvency for organic compounds increases with decreasinganiline point, the use of a granulating agent satisfying the aboverequirement improves the affinity for an organic compound, serving as acarbonaceous material precursor, and allows the organic compound,serving as a carbonaceous material precursor, when mixed with granulatedgraphite particles obtained through this step, to be uniformly depositedon the surface and in the internal voids of the granulated graphite. Inparticular, the granulating agent for use in the present invention,having an aniline point of 80° C. or lower or no aniline point, has highaffinity and compatibility also with an organic compound containing anaromatic compound, for which a granulating agent having a high anilinepoint has low affinity and poor solvency. Thus, even when such anorganic compound containing an aromatic compound is used as acarbonaceous material precursor, the organic compound, serving as acarbonaceous material precursor, when mixed with granulated graphiteparticles obtained through this step, can be uniformly deposited on thesurface and in the internal voids of the granulated graphite.

For example, the aniline point and the mixed aniline point ofhydrocarbon compounds tend to decrease in order of paraffinichydrocarbons, naphthenic hydrocarbons, and aromatic hydrocarbons, andthe aniline point and the mixed aniline point tend to decrease withdecreasing molecular weight.

The aniline point of the granulating agent is typically 80° C. or lower,preferably 50° C. or lower, more preferably 30° C. or lower, still morepreferably 10° C. or lower, particularly preferably 0° C. or lower. Forthe lower limit, some granulating agents have aniline points lower thantheir freezing points, that is, have no aniline point. The properties ofsuch granulating agents having no aniline point can be evaluated bytheir mixed aniline points, and the mixed aniline point is preferably50° C. or lower, more preferably 30° C. or lower, still more preferably20° C. or lower, particularly preferably 0° C. or lower.

The aniline point and the mixed aniline point are determined inaccordance with JIS K2256. The aniline point is defined as a minimumtemperature at which a mixed solution of aniline and a measurementsample (granulating agent) (volume ratio, 1:1) can be in the form of ahomogeneous solution (a temperature at which aniline and the measurementsample (granulating agent) completely mixed with each other begin toseparate and cause turbidity with decreasing temperature). The mixedaniline point is defined as a minimum temperature at which a mixedsolution of aniline, a measurement sample (granulating agent), andheptane (volume ratio, 2:1:1) can be in the form of a homogeneoussolution (a temperature at which aniline, the measurement sample(granulating agent), and heptane completely mixed with each other beginto separate and cause turbidity with decreasing temperature).

Examples of granulating agents include coal tar; petroleum-derived heavyoils; synthetic oils, such as paraffinic oils, including liquidparaffin, olefinic oils, naphthenic oils, and aromatic oils; naturaloils, such as vegetable oils and fats, animal fats, esters, and higheralcohols; organic compounds such as solutions of resin binders inorganic solvents having flash points of 5° C. or higher, preferably 21°C. or higher; aqueous solvents, such as water; and mixtures thereof.Examples of organic solvents having flash points of 5° C. or higherinclude aromatic hydrocarbons, such as alkylbenzenes, including xylene,isopropylbenzene, ethylbenzene, and propylbenzene, alkylnaphthalenes,including methylnaphthalene, ethylnaphthalene, and propylnaphthalene,allylbenzenes, including styrene, and allylnaphthalenes; aliphatichydrocarbons, such as octane, nonane, and decane; ketones, such asmethyl isobutyl ketone, diisobutyl ketone, and cyclohexanone; esters,such as propyl acetate, butyl acetate, isobutyl acetate, and amylacetate; alcohols, such as methanol, ethanol, propanol, butanol,isopropyl alcohol, isobutyl alcohol, ethylene glycol, propylene glycol,diethylene glycol, triethylene glycol, tetraethylene glycol, andglycerol; glycol derivatives, such as ethylene glycol monomethyl ether,ethylene glycol monoethyl ether, ethylene glycol monobutyl ether,diethylene glycol monobutyl ether, triethylene glycol monobutyl ether,tetraethylene glycol monobutyl ether, methoxy propanol, methoxypropyl-2-acetate, methoxymethyl butanol, methoxybutyl acetate,diethylene glycol dimethyl ether, dipropylene glycol dimethyl ether,diethylene glycol ethyl methyl ether, triethylene glycol dimethyl ether,tripropylene glycol dimethyl ether, tetraethylene glycol dimethyl ether,and ethylene glycol monophenyl ether; ethers, such as 1,4-dioxane;nitrogen-containing compounds, such as dimethylformamide, pyridine,2-pyrrolidone, and N-methyl-2-pyrrolidone; sulfur-containing compounds,such as dimethyl sulfoxide; halogen-containing compounds, such asdichloromethane, chloroform, carbon tetrachloride, dichloroethane,trichloroethane, and chlorobenzene; and mixtures thereof, and excludecompounds having low flash points, such as toluene. These organicsolvents can be used alone as a granulating agent. In thisspecification, the flash point can be determined by any known method.

The resin binder may be any known resin binder. For example, use may bemade of cellulose resin binders, such as ethylcellulose,methylcellulose, and salts thereof; acrylic resin binders, such aspolymethyl acrylate, polyethyl acrylate, polybutyl acrylate, polyacrylicacid, and salts thereof; methacryl resin binders, such as polymethylmethacrylate, polyethyl methacrylate, and polybutyl methacrylate; andphenolic resin binders. Among the granulating agents listed above, coaltar, petroleum-derived heavy oils, paraffinic oils, including liquidparaffin, and aromatic oils are preferred because they have high degreesof spheroidization (roundness) and can provide carbon materials thatgenerate little amount of fine powder.

The granulating agent having an aniline point of 80° C. or lower or noaniline point, for its tendency to have a low aniline point, preferablycontains an organic compound having an aromatic and has an averagemolecular weight of preferably 5,000 or less, more preferably 1,000 orless, still more preferably 700 or less, particularly preferably 500 orless. The aniline point can be adjusted also by introducing a functionalgroup having a hetero element such as oxygen or nitrogen.

More preferably, the granulating agent contains an organic compoundhaving a polycyclic aromatic, such as naphthalene, acenaphthylene,acenaphthene, fluorene, anthracene, phenanthrene, and pyrene, becausethese compounds are highly interactive with the basal surface ofgraphite and allow an organic compound, serving as a carbonaceousmaterial precursor, when mixed with granulated graphite particlesobtained through this step, to be more uniformly deposited on thesurface and in the internal voids of the granulated graphite.

Specific examples include synthetic oils, such as olefinic oils,naphthenic oils, and aromatic oils; natural oils, such as vegetable oilsand fats, animal fats, esters, and higher alcohols; coal-derived lightoil fractions produced through the distillation of coal tar, such aslight oil, carbolic oil, creosote oil, naphthalene oil, and anthraceneoil; and mixtures thereof.

Use may also be made of solutions adjusted to have an aniline point of80° C. or lower by diluting a coal-derived raw oil or apetroleum-derived heavy oil, such as coal tar or pitch, with an organicsolvent having a flash point of 5° C. or higher, preferably 21° C. orhigher. Examples of the organic solvent having a flash point of 5° C. orhigher include the organic solvents listed above, and of these organicsolvents, those having an aniline point of 80° C. or lower can be usedalone as a granulating agent.

Among the granulating agents having an aniline point of 80° C. or loweror no aniline point listed above, aromatic oils are more preferredbecause they can provide granulated graphite particles having a highdegree of spheroidization and generating little amount of fine powder,have a good affinity for an organic compound, serving as a carbonaceousmaterial precursor, and allow the organic compound, serving as acarbonaceous material precursor, when mixed with granulated graphiteparticles obtained through this step, to be uniformly deposited on thesurface and in the internal voids of the granulated graphite.

The granulating agent preferably has properties that enable efficientremoval in the step of removing the granulating agent described below(4th step) and have no adverse effect on battery characteristics such ascapacity, input-output characteristics, and storage/cyclecharacteristics. Specifically, those which undergo a weight loss oftypically 50% or more, preferably 80% or more, more preferably 95% ormore, still more preferably 99% or more, particularly preferably 99.9%or more, when heated to 700° C. in an inert atmosphere, can be selectedas appropriate.

Examples of the method of mixing the raw carbon material and thegranulating agent include mixing the raw carbon material with thegranulating agent using a mixer or a kneader; mixing the raw carbonmaterial with the granulating agent in the form of a solution of anorganic compound in a low-viscosity diluted solvent (organic solvent),and then removing the diluted solvent (organic solvent); and mixing theraw carbon material and the granulating agent placed in a granulatorwhile performing granulation in the subsequent 3rd step of granulatingthe raw carbon material.

The amount of granulating agent added is preferably 0.1 part by mass ormore, more preferably 1 part by mass or more, still more preferably 3parts by mass or more, even more preferably 6 parts by mass or more,still even more preferably 10 parts by mass or more, particularlypreferably 12 parts by mass or more, most preferably 15 parts by mass ormore, and preferably 1,000 parts by mass or less, more preferably 100parts by mass or less, still more preferably 80 parts by mass or less,particularly preferably 50 parts by mass or less, most preferably 20parts by mass or less, based on 100 parts by mass of the raw carbonmaterial. Within this range, problems are less likely to occur, such asdecreases in degree of spheroidization due to decreases in interparticleadhesion and decreases in productivity due to the adhesion of the rawcarbon material to apparatuses.

3rd Step: Granulating Raw Carbon Material (Subjecting Raw CarbonMaterial to Spheroidization)

The carbon material is preferably prepared by subjecting a raw carbonmaterial to spheroidization (hereinafter also referred to asgranulation) by applying a mechanical action(s) such as impactcompression, friction, and/or shear force to the raw carbon material.The spheroidized graphite is preferably made of a plurality of flakegraphites or crystalline graphites and ground graphite fine powder,particularly preferably made of a plurality of flake graphites.

One embodiment of the present invention (e.g., but not limited to,Inventions B and J) includes the granulation step of granulating a rawcarbon material by applying at least one type of mechanical energyselected from impact, compression, friction, and shear force.

For this step, for example, apparatuses can be used that repeatedlyapply a mechanical action(s), mainly impact force such as compression,friction, and/or shear force, including the interaction of the rawcarbon material.

Specifically, those apparatuses are preferred which have a rotorequipped with numbers of blades in a casing, the rotor being configuredto rotate at a high speed to apply a mechanical action(s) such asimpact, compression, friction, and/or shear force to a raw carbonmaterial placed in the apparatus, thereby surface treating the rawcarbon material. Furthermore, those apparatuses are preferred which havea mechanism by which a mechanical action(s) is repeatedly applied bycirculating the raw carbon material.

Examples of such apparatuses include Hybridization System (NaraMachinery Co., Ltd.), Kryptron and Kryptron Orb (Earthtechnica Co.,Ltd.), CF Mill (Ube Industries, Ltd.), Mechanofusion System, Nobilta,and Faculty (Hosokawa Micron Corporation), Theta Composer (Tokuju Co.,Ltd.), and COMPOSI (Nippon Coke & Engineering. Co., Ltd). Of these,Hybridization System available from Nara Machinery Co., Ltd. ispreferred.

When the treatment is carried out using any of these apparatuses, forexample, the peripheral speed of the rotor is preferably 30 m/sec ormore, more preferably 50 m/sec or more, still more preferably 60 m/secor more, particularly preferably 70 m/sec or more, most preferably 80m/sec or more, and preferably 100 m/sec or less. A peripheral speed inthis range advantageously enables more efficient spheroidization and, atthe same time, the deposition and the incorporation of fine powder onand into a base material.

Although the mechanical action(s) can be applied to the raw carbonmaterial simply by passing the raw carbon material through theapparatus, preferably, the raw carbon material is circulated through orretained in the apparatus for 30 seconds or more, more preferably 1minute or more, still more preferably 3 minutes or more, particularlypreferably 5 minutes or more.

In the step of granulating the raw carbon material, the raw carbonmaterial may be granulated in the presence of any other substances.Examples of the other substances include metals capable of formingalloys with lithium and oxides thereof, flake graphite, crystallinegraphite, ground graphite fine powder, amorphous carbon, and green coke.Granulation in combination with substances other than the raw carbonmaterial can produce carbon materials for non-aqueous secondarybatteries having various types of particle structures.

The raw carbon material, the granulating agent, and the other substanceseach may be loaded into the above-described apparatus all at one time,sequentially in several times, or continuously. The raw carbon material,the granulating agent, and the other substances may be loaded into theapparatus simultaneously, as a mixture, or individually. The raw carbonmaterial, the granulating agent, and the other substances may be mixedat one time; the other substances may be added to a mixture of the rawcarbon material and the granulating agent; or the raw carbon materialmay be added to a mixture of the other substances and the granulatingagent. Depending on the particle design, they can be added/mixed at anyother appropriate timing.

In spheroidizing the carbon material, it is more preferable to carry outthe spheroidization while depositing and/or incorporating fine powdergenerated during the spheroidization on a base material and/or intospheroidized particles. Carrying out the spheroidization whiledepositing and/or incorporating fine powder generated during thespheroidization on a base material and/or into spheroidized particlescan form a finer intra-particle void structure. As a result, anelectrolyte solution tends to be effectively and efficiently distributedinto the intra-particle voids, and Li-ion insertion/extraction sites inthe particles cannot be efficiently used, thus providing goodlow-temperature output characteristics and cycle characteristics. Thefine powder to be deposited on a base material may be generated duringthe spheroidization, may be generated in adjusting the flake graphiteparticle size, or may be added/mixed at any other appropriate timing.

To deposit and incorporate the fine powder on a base material and intospheroidized particles, it is preferable to enhance flake graphiteparticle-flake graphite particle, flake graphite particle-fine powderparticle, and fine powder particle-fine powder particle adhesive forces.Specific examples of adhesive forces between particles include van derWaals force and electrostatic attraction, which involve no interparticlemediator, and physical and/or chemical cross-linking forces, whichinvolve interparticle mediators.

For Van der Waals force, the relation of “self-weight<adhesion” becomesdistinct as the average particle diameter (d50) decreases from 100 μm.Thus, as the average particle diameter (d50) of the flake graphite, araw material of a spheroidized graphite (raw carbon material),decreases, the interparticle adhesion increases, which advantageouslyfacilitates the deposition and the incorporation of fine powder on abase material and into spheroidized particles. The average particlediameter (d50) of the flake graphite is preferably 1 μm or more, morepreferably 2 μm or more, still more preferably 3 μm or more, preferably80 μm or less, more preferably 50 μm or less, still more preferably 35μm or less, very preferably 20 μm or less, particularly preferably 10 μmor less, most preferably 8 μm or less.

Electrostatic attraction is derived from electrification resulting, forexample, from particle friction, and drier particles tend to be moreeasily electrified and have stronger interparticle adhesion. Thus, theinterparticle adhesion can be enhanced, for example, by reducing thewater content of a graphite before being spheroidized.

The spheroidization is preferably carried out in a low-humidityatmosphere to keep the flake graphite under treatment from absorbingmoisture. Furthermore, to prevent the surface of the flake graphite frombeing oxidized by the energy of a machine process and receiving acidicfunctional groups during the treatment, the spheroidization ispreferably carried out in an inert atmosphere.

Examples of physical and/or chemical cross-linking forces, which involveinterparticle mediators, include physical and/or chemical cross-linkingforces that involve liquid mediators and solid mediators. Examples ofthe chemical cross-linking forces include cross-linking forces ofcovalent bonds, ionic bonds, hydrogen bonds, and other bonds formedbetween particles and interparticle mediators, for example, by chemicalreactions, sintering, and mechanochemical effects.

In one embodiment of the present invention, the spheroidized graphite isprepared by carrying out spheroidization while depositing and/orincorporating fine powder generated by the fracture of a flake graphiteduring the spheroidization on and/or into a parent particle, whereby theparticle strength can be increased to reduce the generation of finepowder upon physical impact. To deposit and/or incorporate the finepowder generated during the spheroidization on and/or into a parentparticle, it is preferable to enhance parent particle-parent particle,parent particle-fine powder, and fine powder-fine powder bindingcapacities. For example, when a flake graphite is spheroidized byrepeatedly applying a mechanical action(s), mainly impact force such ascompression, friction, and/or shear force, including the interaction ofthe target particles, the graphite reacts with oxygen in the atmosphereto generate CO₂ and CO. The inventors intensively studied to discoverthat the parent particle-parent particle, parent particle-fine powder,and fine powder-fine powder binding capacities can be enhanced bycarrying out spheroidization under conditions where the amount of CO₂and CO generated is in a specific range, thereby achieving a carbonmaterial that can provide a high capacity and low-temperature outputcharacteristics when used in a non-aqueous secondary battery.

Specifically, the spheroidization is preferably carried out underconditions where the amount of CO that generates from 1 kg of a flakegraphite is 5 mmol or less, more preferably 4 mmol or less, still morepreferably 3 mmol or less. The lower limit of the amount of CO thatgenerates from 1 kg of a flake graphite can be, for example, but notlimited to, 0.05 mmol or more. The spheroidization is preferably carriedout under conditions where the amount of CO₂ that generates from 1 kg ofa flake graphite is 9 mmol or less, more preferably 8 mmol or less,still more preferably 7 mmol or less. The lower limit of the amount ofCO₂ that generates from 1 kg of a flake graphite can be, for example,but not limited to, 0.1 mmol or more. The spheroidization is preferablycarried out under conditions where the total amount of CO and CO₂ thatgenerate from 1 kg of a flake graphite is 14 mmol or less, morepreferably 12 mmol or less, still more preferably 10 mmol or less. Thelower limit the total amount of CO and CO₂ that generate from 1 kg of aflake graphite can be, for example by but not limited to, 0.15 mmol ormore. Carrying out the spheroidization under conditions within theseranges reduces the amount of graphite functional group of flake graphiteparticles, such as hydroxy (—OH), carboxyl (—C═O(—OH)), carbonyl (C═O),and quinone, which can reduce the obstruction of parent particle-parentparticle, parent particle-fine powder, and fine powder-fine powderbindings, thus providing a carbon material having high particlestrength. As a result, the carbon material used as a negative electrodematerial for a non-aqueous secondary battery generates a reduced amountof fine powder even when a physical impact is applied.

The amount of CO₂ and CO that generate in the spheroidization can becontrolled to be in the above ranges, for example, by reducing theoxygen concentration in an apparatus for applying a mechanical action(s)by purging with an inert gas atmosphere, such as nitrogen, or reducingthe pressure; treating the flake graphite without being exposed tooxygen; adding an auxiliary that is more reactive with oxygen than theflake graphite to preferentially react the auxiliary with oxygen,thereby inhibiting the reaction between the flake graphite and oxygen;or if a raw natural graphite is exposed to oxygen, deoxidizing thegraphite by burning before use. These methods may be combined asappropriate. Alternatively, the spheroidization can be carried out byrepeatedly applying a mechanical action(s), mainly impact force such ascompression, friction, and/or shear force, including the interaction ofthe target particles, to the flake graphite to enhance the parentparticle-parent particle, parent particle-fine powder, and finepowder-fine powder binding capacities, thus reducing the amount ofgraphite functional group.

4th Step: Removing Granulating Agent

One embodiment of the present invention may include the step of removingthe granulating agent. The granulating agent can be removed, forexample, by washing with a solvent or volatilizing/decomposing thegranulating agent by heat treatment.

The heat treatment is carried out preferably at 60° C. or higher, morepreferably 100° C. or higher, still more preferably 200° C. or higher,even more preferably 300° C. or higher, particularly preferably 400° C.or higher, most preferably 500° C. or higher, preferably 1,500° C. orlower, more preferably 1,000° C. or lower, still more preferably 800° C.or lower. A heat treatment temperature in this range can sufficientlyvolatilize/decompose the granulating agent away, leading to improvedproductivity.

The heat treatment is carried out preferably for 0.5 to 48 hours, morepreferably 1 to 40 hours, still more preferably 2 to 30 hours,particularly preferably 3 to 24 hours. A heat treatment time in thisrange can sufficiently volatilize/decompose the granulating agent away,leading to improved productivity.

The atmosphere in the heat treatment may be an active atmosphere, suchas an air atmosphere, or an inert atmosphere, such as a nitrogenatmosphere or an argon atmosphere. When the heat treatment is carriedout at 200° C. to 300° C., there is no particular restriction, but whenthe heat treatment is carried out at 300° C. or higher, it is preferableto use an inert atmosphere, such as a nitrogen atmosphere or an argonatmosphere, to prevent the oxidation of the graphite surface.

5th Step: Increasing Purity of Granulated Carbon Material

One embodiment of the present invention may include the step ofincreasing the purity of the granulated carbon material. The purity ofthe granulated carbon material can be increased, for example, bytreating with acids including nitric acid and hydrochloric acid. Thismethod can advantageously remove impurities in the graphite, such asmetals, metal compounds, and inorganic compounds, without introducingsulfates, which can be highly active sulfur sources, into the system.

For the acid treatment, acids including nitric acid and hydrochloricacid may be used, and use may also be made of other acids, for example,acids made by appropriately mixing inorganic acids, such as bromic acid,hydrofluoric acid, boric acid, and iodine acid, or organic acids, suchas citric acid, formic acid, acetic acid, oxalic acid, trichloroaceticacid, and trifluoroacetic acid. Preferred are concentrated hydrofluoricacid, concentrated nitric acid, and concentrated hydrochloric acid, andmore preferred are concentrated nitric acid and concentratedhydrochloric acid. In the present invention, the graphite may be treatedwith sulfuric acid, provided that sulfuric acid is used in such anamount and at such a concentration that have no adverse effect on theeffects and the physical properties of the present invention.

When different acids are used, for example, the combination ofhydrofluoric acid, nitric acid, and hydrochloric acid is preferredbecause it can efficiently remove the above-described impurities. Forthe mixing ratio of a mixed acid made by combining types of acids asdescribed above, the amount of the fewest component is typically 10% bymass or more, preferably 20% by mass or more, more preferably 25% bymass or more. The upper limit is a value of acids mixed in equal amounts(expressed as 100% by mass/types of acids).

The mixing ratio (by mass) of graphite to acids in the acid treatment istypically 100:10 or greater, preferably 100:20 or greater, morepreferably 100:30 or greater, still more preferably 100:40 or greater,and 100:1,000 or less, preferably 100:500 or less, more preferably100:300 or less. An excessively small ratio tends to fail to efficientlyremove the above-described impurities. An excessively large ratiodisadvantageously reduces the amount of graphite that can be washed atone time, leading to reduced productivity and increased cost.

The acid treatment is carried out by immersing the graphite into anacidic solution as described above. The immersion is carried outtypically for 0.5 to 48 hours, preferably 1 to 40 hours, more preferably2 to 30 hours, still more preferably 3 to 24 hours. An excessively longimmersion tends to lead to reduced productivity and increased cost, andan excessively short immersion tends to fail to sufficiently remove theabove-described impurities.

The immersion is carried out typically at 25° C. or higher, preferably40° C. or higher, more preferably 50° C. or higher, still morepreferably 60° C. or higher. When an aqueous acid is used, thetheoretical upper limit is 100° C., which is the boiling point of water.An excessively low temperature tends to fail to sufficiently remove theabove-described impurities.

To remove a residual acid content after the acid washing to increase thepH from weak acid to neutral, it is preferable to further performwashing with water. For example, when the pH of the graphite washed withacids (the treated graphite) is typically 3 or greater, preferably 3.5or greater, more preferably 4 or greater, still more preferably 4.5 orgreater, washing with water can be omitted, and when the pH is not inthis range, it is preferable to wash the treated graphite with water asrequired. The water used for washing is preferably ion-exchanged wateror distilled water to improve washing efficiency and preventcontamination. A specific resistance, an indicator of ion content of thewater, is typically 0.1 MΩ·cm or more, preferably 1 MSΩ·cm or more,still more preferably 10 MΩ·cm or more. The theoretical upper limit at25° C. is 18.24 MΩ·cm. A small specific resistance means a high ioncontent of the water and tends to lead to contamination and reducedwashing efficiency.

The time for washing with water, that is, stirring the treated graphiteand water is typically 0.5 to 48 hours, preferably 1 to 40 hours, morepreferably 2 to 30 hours, still more preferably 3 to 24 hours. Anexcessively long stirring tends to reduce production efficiency, and anexcessively short stirring tends to increase residual impurities/acidcontent.

The mixing ratio of the treated graphite to water is typically 100:10 orgreater, preferably 100:30 or greater, more preferably 100:50 orgreater, still more preferably 100:100 or greater, and 100:1,000 orless, preferably 100:700 or less, more preferably 100:500 or less, stillmore preferably 100:400 or less. An excessively high ratio tends toreduce production efficiency, and an excessively low ratio tends toincrease residual impurities/acid content.

The stirring is carried out typically at 25° C. or higher, preferably40° C. or higher, more preferably 50° C. or higher, still morepreferably 60° C. or higher. The upper limit is 100° C., which is theboiling point of water. An excessively low temperature tends to increaseresidual impurities/acid content.

When the washing with water is carried out batchwise, the process ofstirring in pure water and filtration is preferably repeated severaltimes to remove impurities/acid content. This process may be carried outrepeatedly until the pH of the above-described treated graphite is inthe above range, typically once or more, preferably twice or more, morepreferably three times or more.

As a result of the above-described treatment, the hydrogen-ionconcentration of waste water of the resulting graphite is typically 200ppm or less, preferably 100 ppm or less, more preferably 50 ppm or less,still more preferably 30 ppm or less, and typically 1 ppm or more,preferably 2 ppm or more, more preferably 3 ppm or more, still morepreferably 4 ppm or more. An excessively high hydrogen-ion concentrationtends to result in a residual acid content to decrease the pH, and anexcessively low hydrogen-ion concentration tends to result in aprolonged treating time to lead to reduced productivity.

5′Th Step: Heat Treating Granulated Carbon Material

The present invention may include the step of heat-treating thegranulated carbon material to adjust its labile carbon content andcrystallinity. Although the labile carbon content on the surface of thecarbon material particles may excessively increase in the granulationdescribed above, the heat treatment can decrease the labile carboncontent to a moderate level.

The temperature condition in the heat treatment is not limited andtypically in the range of 300° C. or higher, preferably 500° C., morepreferably 700° C., particularly preferably 800° C. or higher, andtypically 2,000° C. or lower, preferably 1,500° C. or lower,particularly preferably 1,200° C. or lower, depending on the desireddegree of crystallinity. Such temperature conditions can moderatelyincrease the crystallinity of the surface of the carbon materialparticles.

When the granulated carbon material contains a low-crystallinity carbonmaterial, the low-crystallinity carbon material can be graphitized toincrease its crystallinity in this step for the purpose of increasingdischarge capacity. The temperature condition in the heat treatment isnot limited and typically in the range of 600° C. or higher, preferably900° C. or higher, more preferably 1,600° C. or higher, particularlypreferably 2,500° C. or higher, and typically 3,200° C. or lower,preferably 3,100° C. or lower, depending on the desired degree ofcrystallinity. Such temperature conditions can increase thecrystallinity of the surface of the carbon material particles.

Crystals on the surface of the carbon material particles may bedisordered, and the disorder is particularly pronounced when theabove-described granulation is performed. The heat treatment can repairthe disordered crystals on the surface of the carbon material particles.

In the heat treatment, the retention time during which the temperatureis held in the above range is not limited and typically longer than 10seconds and up to 72 hours.

The heat treatment is carried out in an inert gas atmosphere, such asnitrogen gas, or in a non-oxidizing atmosphere created by the gasgenerated from raw graphite. Examples of apparatuses that can be usedfor the heat treatment include, but are not limited to, shuttlefurnaces, tunnel furnaces, electric furnaces, lead hammer furnaces,rotary kilns, direct energization furnaces, Acheson furnaces, resistanceheating furnaces, and induction heating furnaces.

6th Step: Depositing Carbonaceous Material Having Lower Crystallinitythan Raw Carbon Material on Granulated Carbon Material

One embodiment of the present invention may include the step ofdepositing a carbonaceous material (B) having lower crystallinity thanthe raw carbon material on the granulated carbon material. In otherwords, the above-described carbon material and the carbonaceous material(B) can be combined to form a composite carbon material for the purposeof inhibiting side reactions with an electrolyte solution and improvingfast charge-discharge characteristics. This step can provide a carbonmaterial that can inhibit side reactions with an electrolyte solutionand improve fast charge-discharge characteristics.

The composite graphite obtained by depositing the carbonaceous materialhaving lower crystallinity than the raw carbon material on thegranulated carbon material is also referred to as a “composite carbonmaterial with a carbonaceous material (composite graphite with acarbonaceous material)” or a “composite carbon material”.

Carbonaceous Material (B) Content of Composite Carbon Material

The carbonaceous material (B) content of the composite carbon materialis typically 0.01% by mass or more, preferably 0.1% by mass or more,more preferably 0.5% or more, still more preferably 1% by mass or more,particularly preferably 2% by mass or more, most preferably 3% by massor more, based on the carbon material (A) content. The carbonaceousmaterial (B) content is typically 30% by mass or less, preferably 20% bymass or less, more preferably 15% by mass or less, still more preferably10% by mass or less, particularly preferably 7% by mass or less, mostpreferably 5% by mass or less.

An excessively high carbonaceous material (B) content of the compositecarbon material tends to cause damage to the carbon material (A) tocause material fracture when the composite carbon material is rolledunder a sufficient pressure in order to achieve a non-aqueous secondarybattery having a high capacity, leading to an increased charge-dischargeirreversible capacity in an initial cycle and reduced initialefficiency. An excessively low content tends to be less likely toproduce an effect of the coating.

The carbonaceous material (B) content of the composite carbon materialcan be calculated from sample masses before and after the material isburnt using the equation below. The calculation is made on theassumption that the mass of the carbon material (A) shows no changebefore and after burning.

Carbonaceous material(B)content (% by mass)=[(w2 −w1)/w1]×100

(where w1 is a mass (kg) of the carbon material (A), and w2 is a mass(kg) of the composite carbon material)

When the carbonaceous material (B) is combined by a mixing method, theamount of the carbonaceous material (B) in the composite carbon materialcan be controlled, for example, by the amount of a carbonaceous material(B) precursor added when the carbon material (A) and the carbonaceousmaterial (B) precursor are combined or the residual carbon ratio of thecarbonaceous material (B) precursor. For example, when the residualcarbon ratio of the carbonaceous material (B) precursor, as determinedby a method described in JIS K2270, is p %, the carbonaceous material(B) precursor is added in an amount 100/p times the desired amount ofthe carbonaceous material (B). When the carbonaceous material (B) iscombined by a gas phase method, the amount of the carbonaceous material(B) can be controlled by conditions of the distribution of thecarbonaceous material (B) precursor, such as temperature, pressure, andtime.

X-Ray Parameter of Carbonaceous Material (B)

The carbonaceous material (B) has a d-value (interplanar spacing) oflattice planes ((002) planes), as determined by X-ray diffractometry inaccordance with the method of the Japan Society for Promotion ofScientific Research, of typically 0.3445 nm or less, preferably 0.335 nmto less than 0.340 nm. The d-value is more preferably 0.339 nm or less,still more preferably 0.337 nm or less. A d₀₀₂-value in this rangeincreases the amount of lithium that enters between graphite layers,thus providing a high charge-discharge capacity.

The carbonaceous material (B) has a crystallite size (Lc), as determinedby X-ray diffractometry in accordance with the method of the JapanSociety for Promotion of Scientific Research, in the range of preferably1.5 nm or more, more preferably 3.0 nm or more. A crystallite size inthis range increases the amount of lithium that enters between graphitelayers, thus providing a high charge-discharge capacity. The lower limitof Lc is a theoretical value of graphite.

The X-ray parameter of the carbonaceous material (B) can be analyzed,for example, by heating and burning the carbonaceous material (B)precursor alone to yield the carbonaceous material (B).

Combination with Carbon Material (A)

To load the carbonaceous material (B) onto the surface of the carbonmaterial (A), for example, a precursor of the carbonaceous material (B)is mixed with the carbon material (A), or the carbonaceous material (B)is vapor deposited on the carbon material (A). Particularly preferredmethods include (e.g., but not limited to, Invention F) mixing thecarbon material (A) with an organic compound, serving as a carbonaceousmaterial (B) precursor, so as to be uniformly coated, and heating themixture in a non-oxidizing atmosphere (which is referred to as a mixingmethod in the present invention), and uniformly vapor-depositing amaterial compound for gas phase coating, serving as a carbonaceousmaterial (B) precursor, on the carbon material (A) in an inert gasatmosphere (which is referred to as a gas phase method in the presentinvention). The mixing method and the gas phase method will be describedbelow.

Mixing Method

In the mixing method, the carbon material (A) is mixed with an organiccompound, serving as a carbonaceous material (B) precursor, so as to beuniformly coated, and the mixture is heated in a non-oxidizingatmosphere.

Types of Organic Compound Serving as Carbonaceous Material (B) Precursor

As an organic compound, serving as a carbonaceous material (B)precursor, use can be made of various types of compounds includingcoal-derived heavy oils, such as soft to hard various coal-tar pitches,coal tars, and coal liquefaction oils; petroleum-derived heavy oils,such as residual oils from atmospheric or vacuum distillation of crudeoil; and heavy oils resulting from cracking, such as by-products ofethylene production by naphtha cracking.

In one embodiment of the present invention, petroleum-derived raw oilsand coal-derived raw oils, which have a good affinity for granulatingagents having aniline points of 80° C. or lower and allow the organiccompound, serving as a carbonaceous material precursor, to be uniformlydeposited on the surface of a granulated graphite, are suitable for use,and coal-derived raw oils are particularly suitable for use.

Examples of resin-derived organic compounds include thermosettingresins, such as phenolic resins, polyacrylonitriles, and polyimides;thermoplastic resins, such as polyvinyl chlorides, polyvinylidenechlorides, and polyvinyl alcohols; and natural polymers, such ascelluloses, starch, and polysaccharides.

Examples of coal-derived raw oils that can be used include coal-derivedheavy oils produced from coal, such as coal-tar pitches, impregnatingpitches, molded pitches, and coal liquids; and refined coal-tar pitchesproduced by removing insolubles in coal-tar pitches. Coal-derived rawoils contain large amounts of flat aromatic hydrocarbons formed ofnumbers of benzene rings bonded to each other, such as dibenzocoroneneand pentacene. When aromatic hydrocarbons having flat structures areheated in the burning step to be more flowable, planes of the aromatichydrocarbons having flat structures tend to be superposed on each other,and a thermal polycondensation reaction proceeds with the flatstructures superposed on each other. As a result, the van der Waalsforce between the planes of the hydrocarbons polymerized by thepolycondensation tends to be enhanced to reduce the plane-to-planedistance between the polymerized hydrocarbons, resulting in a higherdegree of crystallinity.

Examples of petroleum-derived raw oils include residual oils from adistillation of heavy oils, residual oils from naphtha cracking, andcatalytically cracked heavy oils. Other examples include heat-treatedpitches obtained by heat treating heavy oils resulting from cracking,such as ethylene tar pitch, FCC decant oil, and Ashland pitch. It isknown that petroleum-derived raw oils, although containing flat aromatichydrocarbons formed of numbers of benzene rings bonded to each other,contain large amounts of linear paraffinic hydrocarbons; moreover, theflat aromatic hydrocarbons formed of numbers of benzene rings bonded toeach other often have pendant methyl or other groups, and some of thebenzene rings are often substituted with cyclohexane rings. Thus, whenaromatic hydrocarbons having flat structures are heated in the burningstep to be more flowable and planes of the aromatic hydrocarbons havingflat structures are superposing on each other, the large amounts oflinear paraffins on the planes tend to obstruct the superposition. Theflat aromatic hydrocarbons having pendant methyl or other groups tend tohinder the superposition of the flat aromatic hydrocarbons. Thecyclohexane rings also tend to obstruct the superposition of thearomatic hydrocarbons, and the cyclohexane rings tend to be pyrolyzed tobe pendant methyl or other groups, further obstructing thesuperposition. These facts suggest that coal-derived raw oils, ascompared with petroleum-derived raw oils, tend to crystallize to ahigher degree and thus are suitable for use as the organic compound,serving as a carbonaceous material precursor, for use in the presentinvention.

Specifically, preferred are petroleum-derived heavy oils produced in oilrefining and coal-derived raw oils produced using coal tar, which isproduced when coke for ironmaking is produced, as a starting material,and more preferred are pitches called a soft pitch or a middle pitchhaving a softening point of 0° C. or higher, preferably 30° C. to 100°C., which are recovered from a column bottom during the distillation ofcoal tar. The organic compound, serving as a carbonaceous materialprecursor, of the present invention may be a mixture of thesecoal-derived raw oils and petroleum-derived raw oils, resin-derivedorganic compounds, and other solvents.

These coal-derived raw oils, which typically contain a light oilfraction, are preferably refined by distillation to extract usefulfractions and improve productivity.

Physical Properties of Organic Compound, Serving as CarbonaceousMaterial (B) Precursor

The organic compound, serving as a carbonaceous material (B) precursor,may be any compound as long as a carbonaceous powder obtained by burningand crushing the organic compound, serving as a carbonaceous material(B) precursor, in an inert atmosphere at 1,300° C. has an interplanarspacing of the crystallite (002) plane (d₀₀₂), as determined bywide-angle X-ray diffractometry in accordance with the method of theJapan Society for Promotion of Scientific Research, of 0.3445 nm orless. A description will be given below of physical properties and aproduction method of a coal-derived raw oil, a preferred organiccompound, by way of illustration and not by way of limitation.

Quinoline Insoluble (Hereinafter Referred to as Qi) Content and β-ResinContent

The Qi content of the organic compound, serving as a carbonaceousmaterial (B) precursor, is typically 0% by mass or more, and typically30% by mass or less, preferably 20% by mass or less, more preferably 15%by mass or less, still more preferably 10% by mass or less, particularlypreferably 5% by mass or less, most preferably 1% by mass or less. Theβ-resin content of the organic compound, serving as a carbonaceousmaterial precursor, is typically 1% by mass or more, preferably 2% bymass or more, more preferably 3% by mass or more, and typically 80% bymass or less, preferably 70% by mass or less, more preferably 60% bymass or less, still more preferably 50% by mass or less, particularlypreferably 30% by mass or less, most preferably 15% by mass or less.

Within the above ranges, composite particles for a non-aqueous secondarybattery can be obtained which has a good-quality carbon structure due togood crystal growth during the carbonization by burning and has astructure in which graphite particles are uniformly coated with acarbonaceous material due to the high affinity for the above-describedgranulating agent, and thus excellent low-temperature outputcharacteristics and high-temperature storage characteristics tend to beexhibited.

The Qi content and the β-resin content can be determined by the methoddescribed below.

If the organic compound, serving as a carbonaceous material (B)precursor, contains a large amount of Qi, crystals will growinsufficiently during the process of carbonization by burning, resultingin poor-quality carbon. Thus, it is preferable to remove Qi from theorganic compound, serving as a carbonaceous material (B) precursor,before carbonization in advance.

Qi can be removed by any known method such as centrifugation, masssedimentation, or filtration. To reduce residual Qi, Qi is preferablyremoved by filtration or mass sedimentation. In this case, anappropriate solvent may optionally be used to facilitate operations.When Qi is removed by filtration, it is carried out under the conditionsof a pressure of typically 0.05 to 1.0 MPa, preferably 0.1 to 0.5 MPa,and a temperature of 20° C. to 200° C., preferably 50° C. to 150° C. Theopening size of a filter used for the filtration is preferably 3 micronsor less.

When Qi is removed by mass sedimentation, it is carried out under theconditions of a temperature of typically 20° C. to 350° C. and astanding time of typically 10 minutes to 10 hours.

After the Qi removal treatment has been performed as described above,the Qi content of the organic compound, serving as a carbonaceousmaterial precursor, is typically 0.1% by mass or less, preferably 0.01%by mass or less. After the Qi removal operation, the β-resin content ofthe organic compound, serving as a carbonaceous material precursor, istypically 1.0 to 15.0% by mass, preferably 4.0 to 10.0% by mass.

Qi Content, β-Resin Content, and Measuring Method

Quinoline (purity: 95.0% or more, available from Wako Pure ChemicalIndustries, Ltd.) and toluene (purity: 99.5% or more, available fromWako Pure Chemical Industries, Ltd.) were provided as solvents, andinsolubles of the organic compound, serving as a carbonaceous materialprecursor, in each solvent are measured by the following procedures (1)to (6).

(1) Take 2.0 g of a sample (e.g., coal tar or coal-tar pitch) into aflask and precisely weigh it (W1).

(2) Pour 100 mL of the above-described measurement solvent (e.g.,quinoline) into the flask containing the sample, attach a condenser, andput the flask into an oil bath at 110° C. (130° C. in the case oftoluene). Heat the solution with stirring for 30 minutes to dissolve thesample in the solvent.

(3) Attach filter paper (W2) precisely weighed in advance to a filter.Pour the solution obtained in (2) into the filter and perform suctionfiltration. Pour 100 mL of the measurement solvent heated at 60° C. ontothe filtration residue to dissolve and wash it. Repeat this operationfour times.

(4) Dry the filtration residue on the filter paper in a dryer at 110° C.for 60 minutes.

(5) Remove the filtration residue on the filter paper from the dryer,allow it to cool in a desiccator for 30 minutes, and then preciselyweigh its weight (W3).

(6) Calculate the solvent insoluble by the following equation.

Solvent insoluble (% by mass)=(residue weight after dissolution/sampleweight)×100=((W3−W2)/W1)×100

The measurements were made according to the above procedure (1) to (6)using various measurement solvents: acetone, quinoline, nitrobenzene,morpholine, and toluene. Insolubles (% by mass) in these solvents arerespectively referred to as acetone insoluble, quinoline insoluble,nitrobenzene insoluble, morpholine insoluble, and toluene insoluble.

Based on the insoluble measured for each solvent, β, α, and β1 can beobtained as follows:

β (toluene insoluble that is soluble in quinoline)=(tolueneinsoluble)−(quinoline insoluble)

α (acetone insoluble that is soluble in toluene)=(acetoneinsoluble)−(toluene insoluble)

β1 (morpholine insoluble that is soluble in nitrobenzene)=(morpholineinsoluble)−(nitrobenzene insoluble)

In the present invention, a soluble in each solvent is a value obtainedby subtracting the insoluble (% by mass) measured by the above methodfrom 100 (% by mass).

Specific Gravity

The lower limit of the specific gravity of the organic compound, servingas a carbonaceous material (B) precursor, is typically 1.1 or greater,preferably 1.14 or greater, more preferably 1.17 or greater, still morepreferably 1.2 or greater. The upper limit is typically 1.5 or less,preferably 1.45 or less, more preferably 1.4 or less, still morepreferably 1.35 or less. An excessively small specific gravity tends toincrease the amount of linear paraffinic hydrocarbon in the organiccompound, leading to low crystallinity in the carbonization by burning.An organic compound having an excessively large specific gravity tendsto have a high molecular weight and a high melting point. An organiccompound having an excessively high melting point, when mixed withgraphite particles to deposit the organic compound on the graphiteparticles in the 6th step of the method for producing a carbon materialfor a non-aqueous secondary battery, the step of depositing acarbonaceous material having lower crystallinity than a raw carbonmaterial on a granulated carbon material, tends to mix with the graphiteparticles ununiformly. The specific gravity is a value at 15° C.

Softening Point

The upper limit of the softening point of the organic compound, servingas a carbonaceous material (B) precursor, is typically 400° C. or lower,preferably 200° C. or lower, more preferably 150° C. or lower, stillmore preferably 100° C. or lower. The lower limit of the softening pointof the organic compound is typically 0° C. or higher, preferably 25° C.or higher, more preferably 30° C. or higher, still more preferably 40°C. or higher. A softening point over the upper limit can make itdifficult to uniformly mix with graphite particles, thus necessitatingmixing at a higher temperature and leading to low productivity. Anorganic compound having a softening point below the lower limit tends tocontain flat aromatic hydrocarbons in a small amount and linearparaffinic hydrocarbons in a relatively large amount and tends toprovide a carbonaceous material coating, obtained by carbonization byburning, with low crystallinity and a carbon material for an non-aqueoussecondary battery with a high specific surface area.

The organic compound, serving as a carbonaceous material (B) precursor,has a residual carbon ratio of typically 1% or more, preferably 10% ormore, more preferably 20% or more, still more preferably 30% or more,particularly preferably 45% or more, and typically 99% or less,preferably 90% or less, more preferably 70% or less, still morepreferably 60% or less. The residual carbon ratio can be measured by amethod in accordance with JIS 2270, for example. A residual carbon ratioin this range tends to enable uniform diffusion and permeation on thesurface and into micropores of the carbon material (A) and enable thesurface and the micropores of the carbon material (A) to be moreuniformly coated with the carbonaceous material (B), thus making itpossible to control the average value and the standard deviation (σ_(R))of microscopic Raman R values to be in the preferred ranges of thepresent invention, leading to improved input-output characteristics.

The addition amount of the carbonaceous material (B) precursor by volume(=mass/density) is typically at least 0.1 time the cumulative porevolume at pore diameters in a range of 0.01 μm to 1 μm of the carbonmaterial (A), preferably at least 0.5 time, more preferably at least 0.7time, still more preferably at least 0.8 time, particularly preferablyat least 0.9 time, most preferably at least 0.95 time, and typically upto 10 times, preferably up to 5 times, more preferably up to 3 times,still more preferably up to 2 times, particularly preferably up to 1.4times, most preferably up to 1.2 times. An addition amount in this rangetends to enable sufficient permeation into pores of the carbon material(A) having a diameter in the range of 0.01 μm to 1 μm and prevent theexcess carbonaceous material (B) precursor from overflowing the pores tobe maldistributed on the surface of the carbon material (A), thusenabling the carbonaceous material (B) precursor to more uniformlydiffuse and permeate on the surface and into the micropores of thecarbon material (A), which allows the average value and the standarddeviation (σ_(R)) of microscopic Raman R values of 30 randomly selectedcomposite carbon materials to be controlled within the preferred rangesof the embodiment of the present invention.

Furthermore, the carbonaceous material (B) precursor can be diluted byadding a solvent or the like as required. Adding a solvent or the liketends to reduce the viscosity of the carbonaceous material (B)precursor, thereby improving the permeability into the pores of thecarbon material (A) having a diameter in the range of 0.01 μm to 1 μm,as a result of which the carbonaceous material (B) precursor moreuniformly diffuses and permeates on the surface and into the microporesof the carbon material (A).

The organic compound, serving as a carbonaceous material (B) precursor,can be mixed with the granulated carbon material by any method, forexample, by mixing the granulated carbon material and the organiccompound, serving as a carbonaceous material (B) precursor, using acommercially available mixer, kneader, or the like to obtain a mixturein which the organic compound is deposited on the granulated carbonmaterial.

The granulated carbon material, the organic compound, serving as acarbonaceous material (B) precursor, and other raw materials such assolvents optionally added are mixed under heating as required. As aresult, the organic compound, serving as a carbonaceous material (B)precursor, in liquid form is deposited on the granulated carbonmaterial. The mixing may be carried out in such a manner that all of theraw materials are charged into a mixer, and mixing and heating areperformed at the same time, or that components other than the organiccompound, serving as a carbonaceous material (B) precursor, are chargedinto a mixer and preheated with stirring, and after the temperature hasincreased to a mixing temperature, the organic compound, serving as acarbonaceous material precursor, at normal temperature or preheated tobe molten is added. To prevent the organic compound, serving as acarbonaceous material (B) precursor, when brought into contact with thegranulated graphite particles, from being cooled to have an increasedviscosity and form an ununiform coating, the mixing is preferablycarried out in such a manner that components other than the organiccompound, serving as a carbonaceous material (B) precursor, are chargedinto a mixer and preheated with stirring, and after the temperature hasincreased to a mixing temperature, the organic compound, serving as acarbonaceous material (B) precursor, preheated to a mixing temperatureto be molten is added.

The heating is carried out typically at a temperature equal to or higherthan the softening point of the organic compound, serving as acarbonaceous material (B) precursor, preferably a temperature higherthan the softening point by 10° C. or more, more preferably atemperature higher than the softening point by 20° C. or more, stillmore preferably by 30° C. or more, particularly preferably by 50° C. ormore, and typically 450° C. or lower, preferably 250° C. or lower. Anexcessively low heating temperature may increase the viscosity of theorganic compound, serving as a carbonaceous material (B) precursor, tomake it difficult to perform mixing, resulting in an ununiform coating.An excessively high heating temperature may cause the organic compound,serving as a carbonaceous material (B) precursor, to be volatilized andpolycondensed, which increases the viscosity of the mixing system tomake it difficult to perform mixing, resulting in an ununiform coating.

The mixer is preferably of a type having a stirring blade, and forexample, use can be made of commercially available products such asribbon mixers, MC processors, plowshare mixers, and KRC kneaders. Themixing is carried out typically for 1 minute or more, preferably 2minutes or more, more preferably 5 minutes or more, and typically 300minutes or less, preferably 120 minutes or less, more preferably 80minutes or less. An excessively short mixing may form an ununiformcoating, and an excessively long mixing tends to cause reducedproductivity and increased cost.

Although the heating temperature (burning temperature) varies dependingon the carbonaceous material (B) precursor used to prepare the mixture,the heating is typically carried out at 800° C. or higher, preferably900° C. or higher, more preferably 950° C. or higher, to achievesufficient amorphous carbonization or graphitization. The upper limit ofthe heating temperature is a temperature at which a carbide of thecarbonaceous material (B) precursor does not form a crystal structureequivalent to the crystal structure of a flake graphite, which is thecarbon material (A) in the mixture, and typically up to 3,500° C. Theupper limit of the heating temperature is 3,000° C., preferably 2,000°C., more preferably 1,500° C.

To prevent oxidation, the heat treatment is performed under a stream ofan inert gas, such as nitrogen or argon, or in a non-oxidizingatmosphere in which gaps are filled with a granular carbon material,such as breeze or packing coke. The equipment used for the heattreatment may be any equipment that suits the above purpose, includingreaction vessels such as shuttle furnaces, tunnel furnaces, lead hammerfurnaces, rotary kilns, and autoclaves, cokers (heat treatment vesselsfor coke production), electric furnaces, gas furnaces, and Achesonfurnaces for electrode materials. The heating rate, the cooling rate,the heat treatment time, and other conditions can be freely selectedwithin the allowable range of the equipment used.

Gas Phase Method

Examples of gas phase methods include processes such as chemical vapordeposition (CVD) in which a material compound for gas phase coating,serving as a carbonaceous material (B) precursor, is uniformly vapordeposited on the surface of the carbon material (A) in an inert gasatmosphere.

A specific example of the material compound for gas phase coating,serving as a carbonaceous material (B) precursor, that can be used is agaseous compound capable of being decomposed by heat, plasma, or thelike to form the carbonaceous material (B) coating on the surface of thecarbon material (A). Examples of the gaseous compound includeunsaturated aliphatic hydrocarbons, such as ethylene, acetylene, andpropylene; saturated aliphatic hydrocarbons, such as methane, ethane,and propane; and aromatic hydrocarbons, such as benzene, toluene, andnaphthalene. These compounds may be used alone or as a mixture of two ormore gases. The temperature, pressure, time, and other conditions in theCVD process can be appropriately selected depending on the type ofcoating material used and the desired amount of the carbonaceousmaterial (B) coating.

When the carbon material (A) is combined with the carbonaceous material(B) by the gas phase method, adjusting the cumulative pore volume andthe pore diameter (e.g., cumulative pore volume at pore diameters in arange of 0.01 μm to 1 μm of the carbon material (A), 0.07 mL/g or more;PD/d50(%), 1.8 or less) enables diffusion via the pores to contactportions between the carbon material (A) particles and into theparticles where the material compound for gas phase coating can hardlyreach, thus enabling the surface and the micropores of, the carbonmaterial (A) to be more uniformly coated with the carbonaceous material(B), which allows the average value and the standard deviation (σ_(R))of microscopic Raman R values of 30 randomly selected composite carbonmaterials to be easily controlled within the preferred ranges of thepresent invention.

Other Steps

After the mixing method or the gas phase method described above isperformed, processes such as disintegration and/or crushing andclassification can be optionally performed to provide a composite carbonmaterial of the present invention.

The composite carbon material may be of any shape and typically has anaverage particle diameter of 2 to 50 μm, preferably 5 to 35 μm,particularly preferably 8 to 30 μm. To achieve the particle diameter inthis range, disintegration and/or crushing and/or classification areperformed as required.

As long as the effect of the embodiment is not adversely affected, otheradditional steps may be performed, or control conditions not describedabove may be added.

According to the production method according to one embodiment of thepresent invention, carbon materials having various types of particlestructures can be stably produced. Typical particle structures includecarbon materials produced by folding a flake graphite, a raw carbonmaterial, having a large or medium average particle diameter, carbonmaterials produced by granulating (folding) a flake graphite having asmall average particle diameter, and carbon materials produced bydepositing an artificial graphite on a natural graphite.

As an indicator of stable production of such carbon materials havingvarious types of particle structures, the yield expressed as a carbonmaterial weight to total solid material weight ratio (carbon materialweight/total solid material weight) is typically 60% or more, preferably80% or more, more preferably 95% or more.

Mixing with Other Carbon Materials

To improve the orientation of electrode plates, the permeability ofelectrolyte solution, the conductive path, and other properties toimprove cycle characteristics, electrode plate expansion, and othercharacteristics, a carbon material different from the above-describedgranulated carbon material or the above-described composite carbonmaterial can be mixed (hereinafter the carbon material different fromthe granulated carbon material or the composite carbon material is alsoreferred to as an “additional carbon material”, and a carbon materialobtained by mixing the granulated carbon material or the compositecarbon material with the carbon material different from the granulatedcarbon material or the composite carbon material is also referred to asa “mixed carbon material”).

As the additional carbon material, use can be made of a materialselected from natural graphites, artificial graphites, coated graphitesmade of carbon materials and carbonaceous material coatings thereon,amorphous carbons, and carbon materials containing metal particles ormetal compounds. The carbon material (A) may be mixed. These materialsmay be used alone or in any combination and composition of two or morematerials.

Examples of natural graphites that can be used include highly purifiedcarbon materials and spheroidized natural graphites. The highpurification typically means an operation of dissolving away ash,metals, and other impurities in a low-purity natural graphite bytreating in an acid, such as hydrochloric acid, sulfuric acid, nitricacid, or hydrofluoric acid, or performing different acid treatments incombination. Typically, water washing or any other treatment isperformed following the acid treatment to remove the acids used in thehigh purification process. In place of the acid treatment, ahigh-temperature treatment at 2,000° C. or higher may be performed toevaporate off ash, metals, and other impurities. The high-temperatureheat treatment may be performed in a halogen gas atmosphere, such aschlorine gas, to remove ash, metals, and other impurities. Furthermore,these techniques may be used in any combination.

The volume-based average particle diameter (also referred to as theaverage particle diameter for short) of such a natural graphite istypically in the range of 5 μm or more, preferably 8 μm or more, morepreferably 10 μm or more, particularly preferably 12 μm or more, andtypically 60 μm or less, preferably 40 μm or less, particularlypreferably 30 μm or less. An average particle diameter in this rangeadvantageously improves fast charge-discharge characteristics andproductivity.

The BET specific surface area of the natural graphite is typically inthe range of 1 m²/g or more, preferably 2 m²/g or more, and typically 30m²/g or less, preferably 15 m²/g or less. A specific surface area inthis range advantageously improves fast charge-discharge characteristicsand productivity.

The tap density of the natural graphite is typically in the range of 0.6g/cm³ or more, preferably 0.7 g/cm³ or more, more preferably 0.8 g/cm³or more, still more preferably 0.85 g/cm³ or more, and typically 1.3g/cm³ or less, preferably 1.2 g/cm³ or less, more preferably 1.1 g/cm³or less. A tap density in this range advantageously improves fastcharge-discharge characteristics and productivity.

Examples of artificial graphites include particles obtained bygraphitizing a carbon material, and, for example, use can be made ofparticles obtained by burning and graphitizing a single graphiteprecursor particle in powder form and granulated particles obtained byforming, burning, graphitizing, and disintegrating a plurality ofgraphite precursor particles.

The volume-based average particle diameter of such an artificialgraphite is typically in the range of 5 μm or more, preferably 10 μm ormore, and typically 60 μm or less, preferably 40 μm or more, morepreferably 30 μm or less. An average particle diameter in this rangeadvantageously reduces the expansion of electrode plates and improvesproductivity.

The BET specific surface area of the artificial graphite is typically inthe range of 0.5 m²/g or more, preferably 1.0 m²/g or more, andtypically 8 m²/g or less, preferably 6 m²/g or less, more preferably 4m²/g or less. A BET specific surface area in this range advantageouslyreduces the expansion of electrode plates and improves productivity.

The tap density of the artificial graphite is typically in the range of0.6 g/cm³ or more, preferably 0.7 g/cm³ or more, more preferably 0.8g/cm³ or more, still more preferably 0.85 g/cm³ or more, and typically1.5 g/cm³ or less, preferably 1.4 g/cm³ or less, more preferably 1.3g/cm³ or less. A tap density in this range advantageously reduces theexpansion of electrode plates and improves productivity.

Examples of coated graphites made of carbon materials and carbonaceousmaterial coatings thereon that can be used include particles obtained bycoating a natural graphite or an artificial graphite with theabove-described organic compound, serving as a carbonaceous materialprecursor, and burning and/or graphitizing the coated material andparticles obtained by coating a natural graphite or an artificialgraphite with a carbonaceous material by CVD.

The volume-based average particle diameter of such a coated graphite istypically in the range of 5 μm or more, preferably 8 μm or more, morepreferably 10 μm or more, particularly preferably 12 μm or more, andtypically 60 μm or less, preferably 40 μm or less, particularlypreferably 30 μm or less. An average particle diameter in this rangeadvantageously improves fast charge-discharge characteristics andproductivity.

The BET specific surface area of the coated graphite is typically in therange of 1 m²/g or more, preferably 2 m²/g or more, more preferably 2.5m²/g or more, and typically 20 m²/g or less, preferably 10 m²/g or less,more preferably 8 m²/g or less, particularly preferably 5 m²/g or less.A specific surface area in this range advantageously improves fastcharge-discharge characteristics and productivity.

The tap density of the coated graphite is typically 0.6 g/cm³ or more,preferably 0.7 g/cm³ or more, still more preferably 0.8 g/cm³ or more,even more preferably 0.85 g/cm³ or more, and typically 1.3 g/cm³ orless, preferably 1.2 g/cm³ or less, more preferably 1.1 g/cm³ or less. Atap density in this range advantageously improves fast charge-dischargecharacteristics and productivity.

Examples of amorphous carbons that can be used include particlesobtained by burning a bulk mesophase and particles obtained byinfusibilizing and burning a readily graphitizable organic compound.

The volume-based average particle diameter of such an amorphous carbonis typically in the range of 5 μm or more, preferably 12 μm or more, andtypically 60 μm or less, preferably 40 μm or less. An average particlediameter in this range advantageously improves fast charge-dischargecharacteristics and productivity.

The BET specific surface area of the amorphous carbon is typically inthe range of 1 m²/g or more, preferably 2 m²/g or more, more preferably2.5 m²/g or more, and typically 8 m²/g or less, preferably 6 m²/g orless, more preferably 4 m²/g or less. A specific surface area in thisrange advantageously improves fast charge-discharge characteristics andproductivity.

The tap density of the amorphous carbon is typically 0.6 g/cm³ or more,preferably 0.7 g/cm³ or more, more preferably 0.8 g/cm³ or more, stillmore preferably 0.85 g/cm³ or more, and typically 1.3 g/cm³ or less,preferably 1.2 g/cm³ or less, more preferably 1.1 g/cm³ or less. A tapdensity in this range advantageously improves fast charge-dischargecharacteristics and productivity.

Examples of carbon materials containing metal particles or metalcompounds include composite materials of a graphite and a metal selectedfrom the group consisting of Fe, Co, Sb, Bi, Pb, Ni, Ag, Si, Sn, Al, Zr,Cr, P, S, V, Mn, Nb, Mo, Cu, Zn, Ge, In, and Ti or a compound thereof.The metal or compound thereof may be an alloy of two or more metals, andthe metal particles may be alloy particles formed of two or more metalelements. Of these, metals selected from the group consisting of Si, Sn,As, Sb, Al, Zn, and W and compounds thereof are preferred, and Si andSiOx are particularly preferred. The general formula SiOx is made fromSi dioxide (SiO₂) and metal Si (Si), and the value of x is typically0<x<2, preferably 0.2 to 1.8, more preferably 0.4 to 1.6, still morepreferably 0.6 to 1.4. A value of x in this range can provide a highcapacity and also reduce the irreversible capacity due to the bond of Liand oxygen.

From the viewpoint of cycle life, the volume-based average particlediameter of such metal particles is typically 0.005 μm or more,preferably 0.01 μm or more, more preferably 0.02 μm or more, still morepreferably 0.03 μm or more, and typically 10 μm or less, preferably 9 μmor less, more preferably 8 μm or less. An average particle diameter inthis range reduces the volume expansion that accompanies charging anddischarging, thus providing good cycle characteristics while maintainingcharge-discharge capacity.

The BET specific surface area of the metal particles is typically 0.5m²/g to 120 m²/g, preferably 1 m²/g to 100 m²/g. A specific surface areain this range advantageously provides a battery with highcharge-discharge efficiency, a high discharge capacity, quick insertionand extraction of lithium in fast charging and discharging, andexcellent rate characteristics.

Examples of apparatuses used to mix the above-described granulatedcarbon material or the above-described composite carbon material withthe additional carbon material include, but are not limited to, rotarymixers, such as cylindrical mixers, twin-cylindrical mixers, double-conemixers, regular cubic mixers, and hoe mixers; and fixed mixers, such asspiral mixers, ribbon mixers, Muller mixers, Helical Flight mixers,Pugmill mixers, and fluidizing mixers.

Physical Properties of Carbon Material for Non-Aqueous Secondary Battery

A description will be given below of preferred physical properties ofthe carbon material according to an embodiment of the present invention.

Volume-Based Average Particle Diameter (Average Particle Diameter d50)

The volume-based average particle diameter (also referred to as “averageparticle diameter d50” or “median diameter”) of the carbon material ispreferably 1 μm or more, more preferably 3 μm or more, still morepreferably 5 μm or more, even more preferably 8 μm or more, particularlypreferably 10 μm or more, most preferably 12 μm or more. The averageparticle diameter d50 is typically 80 μm or less, preferably 50 μm orless, more preferably 40 μm or less, still more preferably 35 μm orless, even more preferably 31 μm or less, particularly preferably 30 μmor less, most preferably 25 μm or less. An average particle diameter inthis range tends to prevent the increase in irreversible capacity andprevent streaks that can occur during a slurry application, thus leadingto no reduction in productivity.

An excessively small average particle diameter d50 tends to cause anincrease in irreversible capacity and a loss in initial battery capacityof a non-aqueous secondary battery comprising the carbon material. Anexcessively large average particle diameter d50 can cause processdefects such as streaks that occur in a slurry application, degradedhigh-current-density charge-discharge characteristics, and degradedlow-temperature output characteristics.

The average particle diameter d50 is defined as a volume-based mediandiameter determined by suspending 0.01 g of a carbon material in 10 mLof a 0.2% by mass aqueous solution of a polyoxyethylene sorbitanmonolaurate surfactant (e.g., Tween 20 (registered trademark)), placingthe suspension (a measurement sample) in a commercially available laserdiffraction/scattering particle size distribution analyzer (e.g., LA-920available from HORIBA), irradiating the measurement sample withultrasonic waves of 28 kHz at a power of 60 W for 1 minute, and thenperforming a measurement with the analyzer.

Tap Density

The tap density of the carbon material is typically 0.7 g/cm³ or more,preferably 0.75 g/cm³ or more, more preferably 0.8 g/cm³ or more, stillmore preferably 0.83 g/cm³ or more, even more preferably 0.85 g/cm³ ormore, very preferably 0.88 g/cm³ or more, particularly preferably 0.9g/cm³ or more, most preferably 0.95 g/cm³ or more, and preferably 1.3g/cm³ or less, more preferably 1.2 g/cm³ or less, still more preferably1.1 g/cm³ or less.

A tap density in this range prevents streaks that can occur during theformation of an electrode plate, thus leading to improved productivityand excellent fast charge-discharge characteristics. In addition, such atap density tends to inhibit the increase in intraparticle carbondensity, thus providing good rolling properties and making it easy toform a high-density negative electrode sheet.

The tap density is defined as a density calculated from a volume and amass of a sample (carbon material). The volume is determined as follows:using a powder density meter, the carbon material of the presentinvention is dropped through a sieve with openings of 300 μm into acylindrical tap cell with a diameter of 1.6 cm and a volume capacity of20 cm³ to fill up the cell; a tap with a stroke length of 10 mm is given1,000 times; and the volume at this time is measured.

Mode Pore Diameter (PD) in Pore Diameter Range of 0.01 μm to 1 μm

The mode pore diameter (PD) in a pore diameter range of 0.01 μm to 1 μmof the carbon material is a value determined by mercury intrusion(mercury porosimetry) and typically 0.01 μm or more, preferably 0.03 μmor more, more preferably 0.05 μm or more, still more preferably 0.06 μmor more, particularly preferably 0.07 μm or more, and typically 1 μm orless, preferably 0.65 μm or less, more preferably 0.5 μm or less, stillmore preferably 0.4 μm or less, even more preferably 0.3 μm or less,particularly preferably 0.2 μm or less, most preferably 0.1 μm or less.

A mode pore diameter (PD) in the range of 0.01 μm to 1 μm outside thisrange tends to prevent an electrolyte solution from being efficientlydistributed into intra-particle voids and prevent the efficient use ofLi-ion insertion/extraction sites in the particles, thus resulting indegraded low-temperature output characteristics and cyclecharacteristics.

Furthermore, when a composite carbon material is formed, such a modepore diameter (PD) tends to prevent the carbonaceous material (B)precursor from uniformly diffusing and permeating to the surface andinto the micropores of the carbon material (A), thus resulting inreduced coating uniformity of the carbonaceous material (B). This makesit difficult to control the average value and the standard deviation(σ_(R)) of microscopic Raman R values of the composite carbon materialand results in degraded low-temperature output characteristics and cyclecharacteristics.

Cumulative Pore Volume at Pore Diameters in Range of 0.01 μm to 1 μm

The cumulative pore volume at pore diameters in a range of 0.01 μm to 1μm of the carbon material is a value determined by mercury intrusion(mercury porosimetry) and, even when pressure is applied, typically 0.07mL/g or more, preferably 0.08 mL/g or more, more preferably 0.09 mL/g ormore, most preferably 0.10 mL/g or more, and preferably 0.3 mL/g orless, more preferably 0.25 mL/g or less, still more preferably 0.2 mL/gor less, particularly preferably 0.18 mL/g or less.

An excessively small cumulative pore volume at pore diameters in a rangeof 0.01 μm to 1 μm tends to prevent an electrolyte solution frompermeating into the particles and prevent the efficient use of Li-ioninsertion/extraction sites in the particles. This impedes smoothinsertion/extraction of lithium ions in fast charging and dischargingand results in degraded low-temperature output characteristics. Acumulative pore volume within the above range tends to allow anelectrolyte solution to be smoothly and efficiently distributed into theparticles, thus enabling the effective and efficient use of Li-ioninsertion/extraction sites in the particles as well as on the peripheryof the particles during charging and discharging and providing goodlow-temperature output characteristics.

Half Width at Half Maximum of Pore Distribution (log (nm))

The half width at half maximum of pore distribution (log (nm)) of thecarbon material refers to a half width at half maximum at a microporeside of a peak in a pore diameter range of 0.01 μm to 1 μm in a poredistribution (nm), as determined by mercury intrusion (mercuryporosimetry), with a horizontal axis expressed in common logarithm (log(nm)).

(In the Case where the Carbon Material has a d50 of 13 μm or More)

When the carbon material having a d50 of 13 μm or more is a spheroidizedcarbon material made of flake graphite, crystalline graphite, and veingraphite, its half width at half maximum of pore distribution (log (nm))is preferably 0.45 or greater, more preferably 0.5 or greater, stillmore preferably 0.6 or greater, particularly preferably 0.65 or greater,most preferably 0.7 or greater, and preferably 10 or less, morepreferably 5 or less, still more preferably 3 or less, particularlypreferably 1 or less.

(In the Case where the Carbon Material has a d50 of Less than 13 μm)

When the d50 of the carbon material is less than 13 μm, its half widthat half maximum of pore distribution (log (nm)) is preferably 0.01 orgreater, more preferably 0.05 or greater, still more preferably 0.1 orgreater, and preferably 0.33 or less, more preferably 0.3 or less, stillmore preferably 0.25 or less, particularly preferably 0.23 or less.

When the half width at half maximum of pore distribution (log (nm)) isin this range, intra-particle voids in a pore diameter range of 0.01 μmto 1 μm tend to be formed to have a finer structure and thus allow anelectrolyte solution to be smoothly and efficiently distributed into theparticles. This enables the effective and efficient use of Li-ioninsertion/extraction sites in the particles as well as on the peripheryof the particles during charging and discharging, thus providing goodlow-temperature output characteristics and cycle characteristics.

Total Pore Volume

The total pore volume of the carbon material is a value determined bymercury intrusion (mercury porosimetry) and preferably 0.1 mL/g or more,more preferably 0.3 mL/g or more, still more preferably 0.5 mL/g ormore, particularly preferably 0.6 mL/g or more, most preferably 0.7 mL/gor more. The total pore volume of the carbon material is preferably 10mL/g or less, more preferably 5 mL/g or less, still more preferably 2mL/g or less, particularly preferably 1 mL/g or less.

A total pore volume in this range eliminates the need for using anexcess amount of binder in forming an electrode plate and facilitatesthe diffusion of a thickener and a binder in forming an electrode plate.

As an apparatus for the mercury porosimetry, a mercury porosimeter(Autopore 9520 available from Micromeritics Corp.) can be used. A sample(carbon material) is weighed to around 0.2 g and placed in a powdercell. The cell is sealed, and a pretreatment is carried out by degassingthe cell at room temperature under vacuum (50 μmHg or lower) for 10minutes.

Subsequently, mercury is introduced into the cell under a reducedpressure of 4 psia (approximately 28 kPa). The pressure is increasedstepwise from 4 psia (approximately 28 kPa) to 40,000 psia(approximately 280 MPa) and then reduced to 25 psia (approximately 170kPa).

The number of steps in the pressure increase is at least 80. In eachstep, the amount of mercury intrusion is measured after an equilibrationtime of 10 seconds. From the mercury intrusion curve thus obtained, apore distribution is calculated using the Washburn equation.

The calculation is made assuming that the surface tension (γ) of mercuryis 485 dyne/cm, and the contact angle (ψ) is 140°. The average porediameter is defined as a pore diameter at a cumulative pore volume of50%.

Ratio (PD/d50(%)) of Mode Pore Diameter (PD) in Pore Diameter Range of0.01 μm to 1 μm to Volume-Based Average Particle Diameter (d50)

The ratio (PD/d50) of mode pore diameter (PD) in a pore diameter rangeof 0.01 μm to 1 μm to volume-based average particle diameter (d50) ofthe carbon material is expressed by equation (1A) and typically 1.8 orless, preferably 1.80 or less, more preferably 1.00 or less, still morepreferably 0.90 or less, particularly preferably 0.80 or less, mostpreferably 0.70 or less, and typically 0.01 or greater, preferably 0.10or greater, more preferably 0.20 or greater.

PD/d50(%)=mode pore diameter (PD) in a pore diameter range of 0.01 μm to1 μm in a pore distribution determined by mercury intrusion/volume-basedaverage particle diameter (d50)×100  Equation (1A):

A mode pore diameter (PD) in a pore diameter range of 0.01 μm to 1 μmoutside this range tends to prevent an electrolyte solution from beingefficiently distributed into intra-particle voids and prevent theefficient use of Li-ion insertion/extraction sites in the particles,thus resulting in degraded low-temperature output characteristics andcycle characteristics.

Furthermore, when the carbon material is formed into a composite carbonmaterial, such a mode pore diameter (PD) tends to prevent thecarbonaceous material (B) precursor from more uniformly diffusing andpermeating to the surface and into the micropores of the carbon material(A). This makes it difficult to control the average value and thestandard deviation (σ_(R)) of microscopic Raman R values of thecomposite carbon material and results in degraded low-temperature outputcharacteristics and cycle characteristics.

Frequency of Particles of 3 μm or Less

The frequency of particles with a particle diameter of 3 μm or less ofthe carbon material after ultrasonic waves of 28 kHz have been appliedat a power of 60 W for 5 minutes is preferably 1% or more, morepreferably 10% or more, and preferably 60% or less, more preferably 55%or less, still more preferably 50% or less, particularly preferably 40%or less, most preferably 30% or less.

A frequency of particles in this range tends to cause less particledecay and fine powder separation during, for example, kneading forpreparing a slurry, rolling an electrode, and charging and discharging,thus providing good low-temperature output characteristics and cyclecharacteristics.

The frequency of particles with a particle diameter of 3 μm or lessafter ultrasonic waves of 28 kHz have been applied at a power of 60 Wfor 5 minutes is a value determined by mixing 50 mL of a 0.2% by volumeaqueous solution of a polyoxyethylene sorbitan monolaurate surfactant(e.g., Tween 20 (registered trademark)) with 0.2 g of a carbon material,applying ultrasonic waves of 28 kHz at a power of 60 W for apredetermined time using a flow-type particle image analyzer “FPIA-2000available from Sysmex Industrial Corp.”, and then counting the number ofparticles with a detection range set to 0.6 to 400 μm.

Roundness

The roundness of the carbon material according to this embodiment istypically 0.88 or greater, preferably 0.90 or greater, more preferably0.91 or greater, still more preferably 0.92 or greater. The roundness ispreferably 1 or less, more preferably 0.98 or less, still morepreferably 0.97 or less.

A roundness in this range tends to inhibit the degradation ofhigh-current-density charge-discharge characteristics of non-aqueoussecondary batteries. The roundness is defined by the following equation,and a theoretically perfect sphere has a roundness of 1.

A roundness in the above range tends to decrease the degree of flectionof Li-ion diffusivity to smoothen the movement of electrolyte solutionin intra-particle voids and enable moderate contact between the carbonmaterials, thus providing good fast charge-discharge characteristics andcycle characteristics.

Roundness=(perimeter of equivalent circle having the same area asprojected particle shape)/(actual perimeter of projected particle shape)

As the value of the roundness is used a value determined, for example,using a flow-type particle image analyzer (e.g., FPIA available fromSysmex Industrial Corp.) by dispersing about 0.2 g of a sample (carbonmaterial) in a 0.2% by mass aqueous solution (approximately 50 mL) of apolyoxyethylene (20) sorbitan monolaurate surfactant, irradiating thedispersion with ultrasonic waves of 28 kHz at a power of 60 W for 1minute, and then measuring the roundness of particles with a diameter inthe range of 1.5 to 40 μm with a detection range set to 0.6 to 400 μm.The ratio of the perimeter of a circle (equivalent circle) having thesame area as the projected particle shape measured, as the numerator, tothe perimeter of the projected particle shape measured, as thedenominator, is calculated, and the average is calculated to determinethe roundness.

X-Ray Parameter

The d-value (interplanar spacing) of lattice planes ((002) planes) ofthe carbon material, as determined by X-ray diffractometry in accordancewith the method of the Japan Society for Promotion of ScientificResearch, is preferably 0.335 nm to less than 0.340 nm. The d-value ismore preferably 0.339 nm or less, still more preferably 0.337 nm orless, particularly preferably 0.336 nm or less. A d₀₀₂-value in thisrange tends to increase the crystallinity of the graphite, thusinhibiting the increase in initial irreversible capacity. Thetheoretical value of graphite is 0.335 nm.

The crystallite size (Lc) of the carbon material, as determined by X-raydiffractometry in accordance with the method of the Japan Society forPromotion of Scientific Research, is preferably in the range of 30 nm ormore, more preferably 50 nm or more, still more preferably 90 nm ormore, particularly preferably 100 nm or more. A crystallite size in thisrange provides particles having not too low crystallinity, thusproviding a non-aqueous secondary battery the reversible capacity ofwhich is less likely to decrease.

Ash Content

The ash content of the carbon material is preferably 1% by mass or less,more preferably 0.5 W by mass or less, still more preferably 0.1% bymass or less, based on the total mass of the carbon material. The ashcontent is preferably at least 1 ppm.

An ash content in this range can provide a non-aqueous secondary batterythat undergoes only negligible degradation of battery performance due tothe reaction between carbon material and electrolyte solution duringcharging and discharging. In addition, such an ash content does notrequire much time or energy to produce a carbon material and eliminatesthe need for equipment for preventing contamination, thus reducing theincrease in cost.

Furthermore, such an ash content can inhibit the increase in thereactivity of a negative electrode formed using the carbon material withan electrolyte solution to reduce gas generation, thus providing apreferred non-aqueous secondary battery.

BET Specific Surface Area (SA)

The specific surface area (SA) of the carbon material, as determined byBET method, is preferably 1 m²/g or more, more preferably 2 m²/g ormore, still more preferably 3 m²/g or more, particularly preferably 4m²/g or more. The specific surface area (SA) is preferably 30 m²/g orless, more preferably 25 m²/g or less, still more preferably 20 m²/g orless, even more preferably 18 m²/g or less, particularly preferably 17m²/g or less, most preferably 15 m²/g or less.

A specific surface area in this range tends to sufficiently secure siteswhere Li enters and exits, thus providing excellent fastcharge-discharge characteristics and output characteristics, and tendsto moderately control the activity of an active material againstelectrolyte solution, thus inhibiting the increase in initialirreversible capacity, as a result of which a high-capacity battery canbe produced.

Furthermore, such a specific surface area can inhibit the increase inthe reactivity of a negative electrode formed using the carbon materialwith an electrolyte solution to reduce gas generation, thus providing apreferred non-aqueous secondary battery.

The BET specific surface area is defined as a value determined asfollows: using a surface area meter (e.g., a Gemini 2360 specificsurface area analyzer available from Shimadzu Corporation), a carbonmaterial sample is preliminarily vacuum dried under a nitrogen stream at100° C. for 3 hours and then cooled to liquid nitrogen temperature, andusing a nitrogen-helium mixed gas precisely regulated so as to have anitrogen pressure of 0.3 relative to atmospheric pressure, a BETspecific surface area is measured by a nitrogen adsorption BETmultipoint method according to a flowing gas method.

True Density

The true density of the carbon material is preferably 1.9 g/cm³ or more,more preferably 2 g/cm³ or more, still more preferably 2.1 g/cm³ ormore, even more preferably 2.2 g/cm³ or more, and up to 2.26 g/cm³. Theupper limit is the theoretical value of graphite. A true density in thisrange tends to avoid too low carbon crystallinity, thus inhibiting theincrease in initial irreversible capacity of non-aqueous secondarybatteries.

Aspect Ratio

The aspect ratio of the carbon material in powder form is theoretically1 or greater, preferably 1.1 or greater, more preferably 1.2 or greater.The aspect ratio is preferably 10 or less, more preferably 8 or less,still more preferably 5 or less.

An aspect ratio in this range tends to prevent streaks of a slurry (amaterial for forming a negative electrode) containing the carbonmaterial from occurring during the formation of an electrode plate so asto provide a uniform coated surface, thus avoiding degradedhigh-current-density charge-discharge characteristics of non-aqueoussecondary batteries.

The aspect ratio is expressed as A/B, where A is the longest diameter ofa carbon material particle observed in a three-dimensional manner, and Bis the shortest diameter among the diameters orthogonal to the longestdiameter. The observation of the carbon material particle is carried outunder a scanning electron microscope capable of magnifying observation.Fifty carbon material particles immobilized on the surface of a metalhaving a thickness of 50 microns or less are randomly selected. For eachof the particles, A and B are determined while a stage on which thesamples are immobilized is rotated and tilted, and the average value ofA/B is calculated.

Maximum Particle Diameter dmax

The maximum particle diameter dmax of the carbon material is preferably200 μm or less, more preferably 150 μm or less, still more preferably120 μm or less, particularly preferably 100 μm or less, most preferably80 μm or less. A dmax in this range tends to inhibit the occurrence ofprocess defects such as streaks.

The maximum particle diameter is defined as a value of the largestparticle diameter in a particle size distribution obtained in themeasurement of average particle diameter d50.

Raman R Value

The Raman R value of the carbon material is preferably, but notnecessarily, 0.01 or greater, more preferably 0.05 or greater, stillmore preferably 0.1 or greater, particularly preferably 0.15 or greater,most preferably 0.2 or greater. The Raman R value is typically 1 orless, preferably 0.8 or less, more preferably 0.7 or less, still morepreferably 0.6 or less, particularly preferably 0.5 or less, mostpreferably 0.4 or less.

The Raman R value is defined as an intensity ratio (I_(B)/I_(A)) in aRaman spectrum obtained by Raman spectroscopy, where I_(A) is anintensity of peak P_(A) near 1,580 cm⁻¹, and I_(B) is an intensity ofpeak P_(B) near 1,360 cm⁻¹.

As used herein, “near 1,580 cm⁻¹” refers to a range of 1,580 to 1,620cm⁻¹, and “near 1,360 cm⁻¹” a range of 1,350 to 1,370 cm⁻¹.

The Raman R value is an indicator of the crystallinity near the surface(from the particle surface to a depth of about 100 angstroms) of acarbon particle, and smaller Raman R values indicate highercrystallinities or less disordered crystalline states. A Raman R valuein this range tends to reduce the possibility that the crystallinity ofthe surface of the carbon material particles increases and thatcrystals, when the density is increased, are oriented in the directionparallel to a negative electrode plate, thus avoiding degraded loadcharacteristics. Furthermore, such a Raman R value tends to reduce thepossibility that crystals on the particle surface are disordered andinhibit the increase in the reactivity of a negative electrode with anelectrolyte solution, thus avoiding reduced charge-discharge efficiencyand increased gas generation of non-aqueous secondary batteries.

The Raman spectrum described above can be measured using a Ramanspectroscope. Specifically, a sample is loaded by gravity-droppingtarget particles into a measuring cell, and the measuring cell isirradiated with an argon-ion laser beam while being rotated in a planeperpendicular to the laser beam. The measurement conditions are asfollows:

Wavelength of argon-ion laser beam: 514.5 nm

Laser power on sample: 25 mW

Resolution: 4 cm⁻¹

Measurement range: 1,100 cm⁻¹ to 1,730 cm⁻¹

Measurement of peak intensity, measurement of peak half-width:background processing, smoothing processing (convolution by simpleaverage, 5 points)

DBP Absorption

The dibutyl phthalate (DBP) absorption of the carbon material ispreferably 85 mL/100 g or less, more preferably 70 mL/100 g or less,still more preferably 65 mL/100 g or less, particularly preferably 60mL/100 g or less. The DBP absorption is preferably 30 mL/100 g or more,more preferably 40 mL/100 g or more.

A DBP absorption in this range, which means that the carbon material isspheroidized to a sufficient degree, tends to reduce the risk of causingdefects such as streaks when a slurry containing the carbon material isapplied. Also, such a DBP absorption tends to avoid the decrease inreactivity because of the presence of pore structures in the particles.

The DBP absorption is defined as a value obtained by making ameasurement in accordance with JIS K6217 using 40 g of a target material(carbon material) under the conditions of a drip rate of 4 mL/min, arotation speed of 125 rpm, and a torque of 500 N·m. For the measurement,use can be made of a Brabender Model E absorptometer, for example.

Average Particle Diameter d10

The particle diameter corresponding to a cumulative total of 10% fromthe smallest particle (d10) of the carbon material, as measured on avolume basis, is preferably 30 μm or less, more preferably 20 μm orless, still more preferably 17 μm or less, and preferably 1 μm or more,more preferably 3 μm or more, still more preferably 5 μm or more.

A d10 in this range does not lead to too strong an aggregation tendencyof the particles, thus avoiding process defects, such as increases inslurry viscosity, and reduced electrode strength and reduced initialcharge-discharge efficiency of non-aqueous secondary batteries.Furthermore, such a d10 tends to avoid degraded high-current-densitycharge-discharge characteristics and degraded low-temperature outputcharacteristics.

The d10 is defined as a value at which the particle frequency % isaccumulated to 10% from the smallest particle diameter in a particlesize distribution obtained in the measurement of average particlediameter d50.

Average Particle Diameter d90

The particle diameter corresponding to a cumulative total of 90% fromthe smallest particle (d90) of the carbon material, as measured on avolume basis, is preferably 100 μm or less, more preferably 70 μm orless, still more preferably 60 μm or less, even more preferably 50 μm orless, particularly preferably 45 μm or less, most preferably 42 μm orless, and preferably 20 μm or more, more preferably 26 μm or more, stillmore preferably 30 μm or more, particularly preferably 34 μm or more.

A d90 in this range tends to avoid reduced electrode strength andreduced initial charge-discharge efficiency of non-aqueous secondarybatteries and also avoid process defects, such as streaks during theapplication of a slurry, degraded high-current-density charge-dischargecharacteristics, and degraded low-temperature output characteristics.

The d90 is defined as a value at which the particle frequency % isaccumulated to 90% from the smallest particle diameter in a particlesize distribution obtained in the measurement of average particlediameter d50.

The silicon content of the carbon material, as determined by X-rayfluorescence analysis (XRF), is typically 5 ppm or more, preferably 10ppm or more, more preferably 15 ppm or more, still more preferably 20ppm or more, and typically 500 ppm or less, preferably 300 ppm or less,more preferably 200 ppm or less, still more preferably 170 ppm or less,particularly preferably 150 ppm or less, most preferably 100 ppm orless.

A silicon content in this range tends to avoid reduced electrodestrength and reduced initial charge-discharge efficiency of non-aqueoussecondary batteries.

Frequency (%) of Particles with Diameter of 5 μm or Less

In one embodiment of the present invention (e.g., but not limited to,Invention C), Q_(5min) (%), the frequency of particles with a diameterof 5 μm or less of the carbon material after ultrasonic waves of 28 kHzhave been applied at a power of 60 W for 5 minutes, is preferably 40% orless, more preferably 35% or less, still more preferably 30% or less.

Q_(1min) (%), the frequency of particles with a diameter of 5 μm or lessof the carbon material after ultrasonic waves of 28 kHz have beenapplied at a power of 60 W for 1 minute, is preferably 30% or less, morepreferably 27% or less, still more preferably 23% or less.

Furthermore, Q_(10min) (%), the frequency of particles with a diameterof 5 μm or less of the carbon material after ultrasonic waves of 28 kHzhave been applied at a power of 60 W for 10 minutes, is preferably 60%or less, more preferably 50% or less, still more preferably 45% or less,most preferably 40% or less.

Frequencies of particles in these ranges tend to cause less carbonmaterial decay and fine powder separation during, for example, kneadingfor preparing a slurry, rolling an electrode, and charging anddischarging, thus providing good low-temperature output characteristicsand cycle characteristics.

In one embodiment of the present invention (e.g., but not limited to,Invention C), the carbon material for a non-aqueous secondary battery ispreferably a carbon material for a non-aqueous secondary battery capableof occluding and releasing lithium ions and formed from a plurality ofgraphite particles, the carbon material satisfying inequality (1C):

Q _(5min) (%)/D50(μm)≦3.5  (1C)

where Q_(5min) (%) is a frequency (%) of particles with a diameter of 5μm or less determined with a flow-type particle image analyzer after thecarbon material has been irradiated with ultrasonic waves of 28 kHz at apower of 60 W for 5 minutes, and D50 (μm) is a volume-based mediandiameter determined by laser diffraction/scattering after the carbonmaterial has been irradiated with ultrasonic waves of 28 kHz at a powerof 60 W for 1 minute.

The ratio of Q_(5min) (%), a frequency of particles with a diameter of 5μm or less after ultrasonic irradiation for 5 minutes, to D50 (μm), avolume-based median diameter, falling within the range defined byinequality (1C) indicates that the carbon material has so high particlestrength as to generate little amount of fine powder even upon physicalimpact. Thus, the carbon material generates little amount of fine powderwhen used as a negative electrode active material to form an electrodeplate, for example, and generates little amount of separated andisolated fine powder upon repeated charging and discharging of abattery, thus providing a non-aqueous secondary battery, particularly, alithium ion secondary battery, having excellent input-outputcharacteristics and excellent cycle characteristics.

The frequency (%) of particles with a diameter of 5 μm or less afterultrasonic irradiation and the volume-based median diameter in thisspecification are determined as described below.

Frequency (%) of Particles with Diameter of 5 μm or Less afterUltrasonic Irradiation

The frequency (%) of particles with a diameter of 5 μm or less afterultrasonic irradiation is a percentage of the number of particles with adiameter of 5 μm or less in the total, as determined by mixing 50 mL ofa dispersion medium with 0.2 g of a sample, placing the mixture in aflow-type particle image analyzer (e.g., FPIA-2000 available from SysmexIndustrial Corp.), applying ultrasonic waves of 28 kHz at a power of 60W for a predetermined time, and then counting the number of particleswith a detection range set to 0.6 to 400 μm. In this specification, thefrequency (%) of particles with a diameter of 5 μm or less is expressedas Q_(5min) (%), Q_(1min) (%), and Q_(10min) (%) when the ultrasonicirradiation time is 5 minutes, 1 minute, and 10 minutes, respectively.

The dispersion medium may be any medium capable of homogeneouslydispersing the sample in the liquid, and, for example, alcohols, such asethanol and butanol, and water can be used. Dispersant solutionscontaining dispersants can also be used, and examples include 0.2% byvolume aqueous solutions of polyoxyethylene sorbitan monolauratesurfactants (e.g., Tween 20, registered trademark).

Ratio of Frequency of Particles with Diameter of 5 μm or Less(%)/Volume-Based Median Diameter D50 (μm)

In one embodiment of the present invention (e.g., but not limited to,Invention C), the ratio of Q_(5min) (%), a frequency (%) of particleswith a diameter of 5 μm or less after applying ultrasonic waves of 28kHz to the carbon material at a power of 60 W for 5 minutes, to D50(μm), a volume-based median diameter, (Q_(5min)/D50) is 3.5 or less,preferably 3.0 or less, more preferably 2.5 or less. Although the lowerlimit is not limited to a particular value, it can be at least 0.1.

A Q_(5min)/D50 ratio in this range can further reduce the generation offine powder during the formation of an electrode plate and reduces therisk of causing a conductive path break and a side reaction with anelectrolyte solution to increase resistance, thus providing anon-aqueous secondary battery, particularly, a lithium ion secondarybattery, having excellent input-output characteristics. In addition,such a ratio reduces the risk of causing separation and isolation offine powder to cause a conductive path break when the carbon materialparticles swell and shrink upon repeated charging and discharging, thusproviding a non-aqueous secondary battery, particularly, a lithium ionsecondary battery, having excellent cycle characteristics.

The ratio of Q_(1min) (%), a frequency (%) of particles with a diameterof 5 μm or less after applying ultrasonic waves of 28 kHz at a power of60 W for 1 minute, to D50 (μm) (Q_(1min)/D50) is preferably, but notnecessarily, 2.4 or less, more preferably 2.0 or less, still morepreferably 1.8 or less, particularly preferably 1.5 or less. Althoughthe lower limit is not limited to a particular value, it can be at least0.1.

A Q_(1min)/D50 ratio in this range can readily provide a non-aqueoussecondary battery, particularly, a lithium ion secondary battery,comprising a negative electrode active material made of the carbonmaterial, the battery being less likely to undergo separation andisolation of fine powder during charging and discharging to experience aconductive path break and having excellent cycle characteristics.

Furthermore, the ratio of Q_(10min), a frequency (%) of particles with adiameter of 5 μm or less after applying ultrasonic waves of 28 kHz at apower of 60 W for 10 minutes, to D50 (μm) (Q_(10min)/D50) is preferably,but not necessarily, 4.0 or less, more preferably 3.5 or less, stillmore preferably 3.3 or less, particularly preferably 3.0 or less.Although the lower limit is not limited to a particular value, it can beat least 0.1.

A Q_(10min)/D50 ratio in this range can readily provide a non-aqueoussecondary battery, particularly, a lithium ion secondary battery,comprising a negative electrode active material made of the carbonmaterial, the battery being less likely to undergo separation andisolation of fine powder, for example, during charging and dischargingto experience a conductive path break and having excellent cyclecharacteristics.

Total Amount of Eliminated CO and Eliminated CO₂ During Temperature Risefrom Room Temperature to 1,000° C. Using Pyrolysis Mass Spectrometer(TPD-MS)

In one embodiment of the present invention (e.g., but not limited to,Invention C), the total amount of eliminated CO and eliminated CO₂measured using a pyrolysis mass spectrometer (TPD-MS) by heating thecarbon material from room temperature to 1,000° C. is preferably 125μmol/g or less, more preferably 100 μmol/g or less, still morepreferably 75 μmol/g or less. Although the lower limit is not limited toa particular value, it can be at least 1 μmol/g. As used herein, “roomtemperature” means 20° C. to 25° C.

Amount of Eliminated CO During Temperature Rise from Room Temperature to1,000° C. Using Pyrolysis Mass Spectrometer (TPD-MS)

The amount of eliminated CO measured using a pyrolysis mass spectrometer(TPD-MS) by heating the carbon material according to this embodimentfrom room temperature to 1,000° C. is preferably 100 μmol/g or less,more preferably 80 μmol/g or less, still more preferably 60 μmol/g orless. Although the lower limit is not limited to a particular value, itcan be at least 1 μmol/g.

Amount of Eliminated CO₂ During Temperature Rise from Room Temperatureto 1,000° C. Using Pyrolysis Mass Spectrometer (TPD-MS)

The amount of eliminated CO₂ measured using a pyrolysis massspectrometer (TPD-MS) by heating the carbon material according to thisembodiment from room temperature to 1,000° C. is preferably 25 μmol/g orless, more preferably 20 μmol/g or less, still more preferably 15 μmol/gor less. Although the lower limit is not limited to a particular value,it can be at least 1 μmol/g.

Within the above ranges, the amount of graphite functional group, suchas hydroxy (—OH), carboxyl (—C═O(—OH)), carbonyl (C═O), and quinone, ofgraphite particles of the carbon material is small, which reduces theobstruction of parent particle-parent particle, parent particle-finepowder, and fine powder-fine powder bindings that might otherwise becaused by these functional groups, thus providing a carbon materialhaving high particle strength. As a result, the carbon materialgenerates a reduced amount of fine powder even when a physical impact isapplied. In addition, when the carbon material is used as a negativeelectrode of a battery, the small amount of functional group reduces therisk of side reactions with an electrolyte solution, which can reducethe amount of gas generated in the battery.

In one aspect of the carbon material according to an embodiment of thepresent invention, preferred is a carbon material for a non-aqueoussecondary battery capable of occluding and releasing lithium ions, thecarbon material having a cumulative pore volume at pore diameters in arange of 2 to 4 nm, as determined by nitrogen gas adsorption, of 0.0022cm³/g or more and a tap density of 0.83 g/cm³ or more.

In this embodiment (e.g., but not limited to, Invention G), a carbonmaterial or a mixed carbon material is preferred.

Cumulative Pore Volume at Pore Diameters in Range of 2 to 4 nmDetermined by Nitrogen Gas Adsorption

In this embodiment (e.g., but not limited to, Invention G), the carbonmaterial has a cumulative pore volume at pore diameters in a range of 2to 4 nm, as determined by nitrogen gas adsorption, of 0.0022 cm³/g ormore, preferably 0.0025 cm³/g or more, more preferably 0.0028 cm³/g ormore, still more preferably 0.0032 cm³/g or more, particularlypreferably 0.0035 cm³/g or more, and typically 1.0 cm³/g or less,preferably 0.10 cm³/g or less, more preferably 0.050 cm³/g or less,still more preferably 0.010 cm³/g or less, particularly preferably0.0050 cm³/g or less.

A cumulative pore volume at pore diameters in a range of 2 to 4 nm ofthe carbon material smaller than 0.0022 cm³/g results in insufficientlithium insertion/extraction sites, thus leading to a low-temperatureoutput. An excessively large cumulative pore volume tends to increaseside reactions with an electrolyte solution, thus reducing storagecharacteristics and charge-discharge efficiency.

The cumulative pore volume can be determined by nitrogen gas adsorption.As an apparatus for the measurement, an Autoforb (Quantachrome) can beused. A sample is placed in a powder cell, and the cell is sealed andpre-treated at 350° C. under vacuum (1.3 Pa or lower) for 2 hours, afterwhich an adsorption isotherm (adsorption gas: nitrogen) is measured atliquid nitrogen temperature.

Using the adsorption isotherm obtained, a BJH analysis was performed todetermine a micropore distribution, from which the cumulative porevolume at pore diameters in a range of 2 nm to 100 nm is calculated.

Maximum dV/Dlog (D) (V: Cumulative Pore Volume, D: Pore Diameter) atPore Diameters in Range of 2 to 4 nm Determined by Nitrogen GasAdsorption

In one embodiment of the present invention (e.g., but not limited to,Invention G), the maximum dV/dlog (D) (V: cumulative pore volume, D:pore diameter) at pore diameters in a range of 2 to 4 nm of the carbonmaterial, as determined by nitrogen gas adsorption, is typically 0.0090cm³/g or more, preferably 0.011 cm³/g or more, more preferably 0.013cm³/g or more, and typically 0.50 cm³/g or less, preferably 0.10 cm³/gor less, more preferably 0.050 cm³/g or less, still more preferably0.020 cm³/g or less.

A maximum dV/dlog in this range tends to ensure sufficient lithium-ioninsertion/extraction sites, thus effectively improving low-temperatureoutput.

The dV/dlog (D) is a quotient of a differential cumulative pore volumedV divided by the logarithmic differential value d (log D) of a porediameter and is calculated by measuring the above cumulative pore volumeat pore diameters in a range of 2 to 4 nm, as determined by nitrogen gasadsorption, such that the interval of log (D) is 0.010 to 0.050.

Cumulative Pore Volume at Pore Diameters in Range of 2 to 100 nmDetermined by Nitrogen Gas Adsorption

In this embodiment (e.g., but not limited to, Invention G), thecumulative pore volume at pore diameters in a range of 2 to 100 nm ofthe carbon material, as determined by nitrogen gas adsorption, istypically 0.025 cm³/g or more, preferably 0.030 cm³/g or more, morepreferably 0.035 cm³/g or more, still more preferably 0.040 cm³/g ormore, and typically 5.0 cm³/g or less, preferably 2.0 cm³/g or less,more preferably 1.0 cm³/g or less, still more preferably 0.50 cm³/g orless, particularly preferably 0.10 cm³/g or less.

A cumulative pore volume at pore diameters in a range of 2 to 100 nm ofthe carbon material in this range smoothens the movement of electrolytesolution between particles, thus improving input-output characteristics.

The cumulative pore volume at pore diameters in a range of 2 to 100 nmdetermined by nitrogen gas adsorption is calculated by the samemeasurement method as for the above cumulative pore volume at porediameters in a range of 2 to 4 nm.

In one aspect of one embodiment of the present invention, preferred is acarbon material for a non-aqueous secondary battery capable of occludingand releasing lithium ions, the carbon material having a Raman R value,as given by equation (1H), of 0.31 or greater and a thermal weight lossratio per unit area (ΔTG/SA), as given by equation (2H), of 0.05 to0.45.

In other words, the carbon material according to an embodiment of thepresent invention (e.g., but not limited to, Invention H) is preferablya carbon material for a non-aqueous secondary battery capable ofoccluding and releasing lithium ions, the carbon material having a RamanR value, as given by equation (1H), of 0.31 or greater and a thermalweight loss ratio per unit area (ΔTG/SA), as given by equation (2H), of0.05 to 0.45.

Raman value R=intensity I _(B) of peak P _(B) near 1,360 cm-1/intensityI _(A) of peak P _(A) near 1,580 cm-1 by Raman spectrumanalysis  Equation (1H)

(ΔTG/SA)=(thermal weight loss (ΔTG) (%) on heating from 400° C. to 600°C. at 2° C./min in air atmosphere, measured with differential thermalbalance)/(specific surface area (SA) (m²/g) of carbon materialdetermined by BET method)  Equation (2H)

Raman R Value

The Raman R value of the carbon material according to this embodiment(e.g., but not limited to, Invention H), as given by equation (1H), is0.31 or greater, preferably 0.32 or greater, more preferably 0.33 orgreater, still more preferably 0.35 or greater, particularly preferably0.36 or greater, most preferably 0.37 or greater. The upper limit of theRaman R value is typically, but not necessarily, 1 or less, preferably0.7 or less, more preferably 0.6 or less, still more preferably 0.5 orless.

Raman value R=intensity I _(B) of peak P _(B) near 1,360 cm⁻¹/intensityI _(A) of peak P _(A) near 1,580 cm⁻¹ by Raman spectrumanalysis  Equation (1H)

As used herein, “near 1,580 cm⁻¹” refers to a range of 1,580 to 1,620cm⁻¹, and “near 1,360 cm⁻¹” a range of 1,350 to 1,370 cm⁻¹.

A Raman R value of less than 0.31 tends to increase the crystallinity ofthe surface of the carbon material particles to reduce Li-ioninsertion/extraction sites, thus resulting in degraded low-temperatureoutput characteristics. An excessively large Raman R value tends toreduce graphite crystallinity, thus resulting in a low dischargecapacity.

The Raman spectrum described above can be measured using a Ramanspectroscope. Specifically, a sample is loaded by gravity-droppingtarget particles into a measuring cell, and the measuring cell isirradiated with an argon-ion laser beam while being rotated in a planeperpendicular to the laser beam. The measurement conditions are asfollows:

Wavelength of argon-ion laser beam: 514.5 nm

Laser power on sample: 25 mW

Resolution: 4 cm⁻¹

Measurement range: 1,100 cm⁻¹ to 1,730 cm⁻¹

Measurement of peak intensity, measurement of peak half-width:background processing, smoothing processing (convolution by simpleaverage, 5 points)

Thermal Weight Loss Ratio Per Unit Area (ΔTG/SA)

The thermal weight loss (ΔTG) (%) of the carbon material according tothis embodiment (e.g., but not limited to, Invention H) is determined asfollows: into a platinum pan, 5 mg of a carbon material is weighed, andthe pan is placed in a differential thermal balance (TG8120 availablefrom Rigaku Corporation); under an air stream of 100 mL/min, thetemperature is raised from room temperature to 400° C. at a rate of 20°C./min and then from 400° C. to 600° C. at a rate of 2° C./min, and theamount of thermal weight loss is measured. The calculated value ofthermal weight loss between 400° C. and 600° C. in this measurement isdefined as a thermal weight loss (ΔTG) (%) in the present invention. Thethermal weight loss ratio per unit area (ΔTG/SA) is calculated byequation (2H).

The ΔTG/SA is typically 0.05 or greater, preferably 0.08 or greater,more preferably 0.10 or greater, still more preferably 0.13 or greater,particularly preferably 0.15 or greater, most preferably 0.17 orgreater, and typically 0.45 or less, preferably 0.43 or less, morepreferably 0.40 or less, still more preferably 0.35 or less,particularly preferably 0.30 or less, most preferably 0.25 or less.

(ΔTG/SA)=(thermal weight loss (ΔTG) (%) on heating from 400° C. to 600°C. at 2° C./min in air atmosphere, measured with differential thermalbalance)/(specific surface area (SA) (m²/g) of carbon materialdetermined by BET method)  Equation (2H)

A ΔTG/SA of greater than 0.45 reduces graphite crystallinity, thusresulting in a low discharge capacity, and further impedes the smoothmovement of Li ions, thus resulting in degraded low-temperature outputcharacteristics. A ΔTG/SA of less than 0.05 reduces the number of Li-ioninsertion/extraction sites, thus resulting in degraded low-temperatureoutput characteristics.

In this embodiment (e.g., but not limited to, Invention H), a carbonmaterial or a mixed carbon material is preferred.

In one aspect of one embodiment of the present invention, the carbonmaterial is preferably a carbon material for a non-aqueous secondarybattery capable of occluding and releasing lithium ions, the carbonmaterial being graphite particles satisfying the relationship ofinequality (1I).

100Y _(i)+0.26X _(i)>α  Inequality (1I)

(In the inequality, Y_(i) is an oxygen functional group dispersity givenby equation (2I); X_(i) is a volume-based average particle diameter(d50) (μm); and α=9.4)

Oxygen functional group dispersity (Y _(i))=total oxygen content (mol %)determined by elemental analysis/surface oxygen content (O/C) (mol %)determined by X-ray photoelectron spectroscopy  Equation (2I)

Specifically, the carbon material for a non-aqueous secondary batteryaccording to one embodiment of the present invention (e.g., but notlimited to, Invention I) preferably satisfies the relationship ofinequality (1I), which is a relationship between oxygen functional groupdispersity and volume-based average particle diameter (d50).

100Y _(i)+0.26X _(i)>α  Inequality (1I)

(In the inequality, Y_(i) is an oxygen functional group dispersity givenby equation (2I); X_(i) is a volume-based average particle diameter(d50) (μm); and α=9.4)

Oxygen functional group dispersity (Y _(i))=total oxygen content (mol %)determined by elemental analysis/surface oxygen content (O/C) (mol %)determined by X-ray photoelectron spectroscopy  Equation (2I)

The value α given by inequality (1I) of the carbon material according tothis embodiment (e.g., but not limited to, Invention I) is 9.4,preferably 9.5, more preferably 9.6, still more preferably 9.7,particularly preferably 9.8, most preferably 10.0. When the relationshiprepresented by inequality (1I) is unsatisfied, efficient Li-ioninsertion/extraction cannot be effected in the particles, which tends toresult in degraded low-temperature output characteristics and a reducedcapacity.

Surface Functional Group Amount O/C Value (Mol %)

For X-ray photoelectron spectroscopy (XPS), an X-ray photoelectronspectroscope (e.g., ESCA available from Ulvac-Phi, Incorporated) isused. A measuring object (in this case, a graphite material, i.e., thecarbon material) is mounted on a sample stage such that the surface ofthe object is flat, and a multiplex measurement is performed using a Kαradiation of aluminum as an X-ray source to measure spectra of C1s (280to 300 eV) and O1s (525 to 545 eV). Charge correction is performed withthe C1s peak top obtained set to 284.3 eV. Peak areas of the spectra ofC1s and O1s are determined and then multiplied by an apparatussensitivity to determine the surface atom concentrations of C and O. TheO/C ratio of the atom concentrations of O and C obtained (O atomconcentration/C atom concentration)×100 is defined as the surfacefunctional group amount O/C value of the carbon material.

The O/C value determined by XPS is preferably 0.01 or greater, morepreferably 0.1 or greater, still more preferably 0.3 or greater,particularly preferably 0.5 or greater, most preferably 0.7 or greater,and preferably 2 or less, more preferably 1.5 or less, still morepreferably 1.2 or less, particularly preferably 1 or less, mostpreferably 0.8 or less. A surface functional group amount O/C value inthis range tends to enhance the desolvation reactivity of Li ions withan electrolyte solution solvent on the surface of a negative electrodeactive material, thus leading to improved fast charge-dischargecharacteristics, and reduce the reactivity with an electrolyte solution,thus leading to improved charge-discharge efficiency.

Total Oxygen Content (Mol %)

For measuring oxygen/nitrogen/hydrogen contents, anoxygen/nitrogen/hydrogen analyzer (TCH600 ONH determinator availablefrom LECO) is used. In an inert gas atmosphere impulse furnace, 50 mg ofthe carbon material is melted and decomposed, and the amounts of carbonmonoxide and carbon dioxide in a discharged carrier gas are measuredusing an infrared detector to determine the total oxygen content (mol %)of the carbon material.

The total oxygen content (mol %), as determined by the measurement ofoxygen/nitrogen/hydrogen contents, is preferably 0.001 mol % or more,more preferably 0.01 mol % or more, still more preferably 0.02 mol % ormore, particularly preferably 0.03 mol % or more, most preferably 0.04mol % or more, and preferably 0.5 mol % or less, more preferably 0.2 mol% or less, still more preferably 0.15 mol % or less, particularlypreferably 0.1 mol % or less, most preferably 0.08 mol % or less. Atotal oxygen content (mol %) in this range tends to promote thedesolvation reaction of Li ions with an electrolyte solution solvent onthe surface of a negative electrode active material, thus leading toimproved fast charge-discharge characteristics, and reduce thereactivity with an electrolyte solution, thus leading to improvedcharge-discharge efficiency.

Y_(i): Oxygen Functional Group Dispersity

The oxygen functional group dispersity of the carbon material istypically 0.01 or greater, preferably 0.04 or greater, more preferably0.06 or greater, still more preferably 0.07 or greater, and typically 1or less, preferably 0.5 or less, more preferably 0.3 or less, still morepreferably 0.2 or less.

An oxygen functional group dispersity in this range means that oxygenfunctional groups are not maldistributed on the particle surface anddispersed also in the particles. The presence of oxygen functionalgroups at graphite crystal edge portions that functions as Li-ioninsertion/extraction sites suggests that the carbon material having anoxygen functional group dispersity in this range has a moderate numberof Li-ion insertion/extraction sites not only on but also in theparticles. Thus, an oxygen functional group dispersity in this rangeenables efficient Li-ion insertion/extraction also in the particles andtends to provide a high capacity and good low-temperature outputcharacteristics.

In this embodiment (e.g., but not limited to, Invention I), a carbonmaterial or a mixed carbon material is preferred.

In one aspect of one embodiment of the present invention, the carbonmaterial for a non-aqueous secondary battery is a carbon material for anon-aqueous secondary battery characterized in that a large number ofvoids having fine structures are present in the particles.

Specifically, the carbon material for a non-aqueous secondary batteryaccording to an embodiment of the present invention (e.g., but notlimited to, Inventions L¹ to L³) preferably comprises a carbon materialmade of granulated particles satisfying (1L) and (2L) and further has acharacteristic particle cross section such that a box-counting dimensionis determined from an image of the particle cross section.

Carbon Material (Granulated Particles) Satisfying (1L) and (2L) inCarbon Material for Non-Aqueous Secondary Battery

The granulated particles in the carbon material for a non-aqueoussecondary battery satisfies the following:

(1) Being made of a carbonaceous material; and

(2) Satisfying the relationship |X₁−X|/X₁≦0.2, preferably ≦0.15, morepreferably ≦0.1, where X is a volume-based average particle diameterdetermined by laser diffraction, and X₁ is an equivalent circulardiameter determined from a cross-sectional SEM image.

If |X₁−X|/X₁ is too large, typical particles cannot be selected, whichmay result in failure to express the overall tendency.

The volume-based average particle diameter X is defined as avolume-based median diameter determined by suspending 0.01 g of a carbonmaterial in 10 mL of a 0.2% by mass aqueous solution of apolyoxyethylene sorbitan monolaurate surfactant (e.g., Tween 20(registered trademark)), placing the suspension (a measurement sample)in a commercially available laser diffraction/scattering particle sizedistribution analyzer (e.g., LA-920 available from HORIBA), irradiatingthe measurement sample with ultrasonic waves of 28 kHz at a power of 60W for 1 minute, and then performing a measurement with the analyzer.

The equivalent circular diameter X₁ determined from a cross-sectionalSEM image is expressed by the following formula using a particlecircumference L [μm].

$\begin{matrix}{X_{1} = \frac{L}{2\pi}} & \left\lbrack {{Mathematical}\mspace{14mu} 1} \right\rbrack\end{matrix}$

The granulated particles in the carbon material for a non-aqueoussecondary battery satisfies the relationship |R−R₁|≦0.1, preferably≦0.08, more preferably ≦0.06, where R is a roundness determined with aflow-type particle image analyzer, and R₁ is a roundness determined froma cross-sectional SEM image.

If |R−R₁| is too large, a particle boundary is not defined correctly butoverestimated, which may result in incorrect analysis.

As the value of the roundness R determined with a flow-type particleimage analyzer is used a value determined, for example, using aflow-type particle image analyzer (e.g., FPIA available from SysmexIndustrial Corp.) by dispersing about 0.2 g of a sample (carbon materialfor a non-aqueous secondary battery) in a 0.2% by mass aqueous solution(approximately 50 mL) of a polyoxyethylene (20) sorbitan monolauratesurfactant, irradiating the dispersion with ultrasonic waves of 28 kHzat a power of 60 W for 1 minute, and then measuring the roundness ofparticles with a diameter in the range of 1.5 to 40 μm with a detectionrange set to 0.6 to 400 μm.

The roundness R₁ determined from a cross-sectional SEM image iscalculated by the following formula using a particle area S [μm²]determined from a cross-sectional SEM image and a circumference L [μm].

$\begin{matrix}{R_{1} = \frac{4\; \pi \; S}{(L)^{2}}} & \left\lbrack {{Mathematical}\mspace{14mu} 2} \right\rbrack\end{matrix}$

The particle boundary may be defined by any method, and it may bedefined automatically or manually using commercially available analysissoftware. It is preferable to approximate a particle by a polygon, andin this case, an approximation by a polygon with 15 or more sides ismore preferred. This is because if a polygon with less than 15 sides isused, a background portion may be determined to be a part of theparticle in approximating a curve.

Acquisition of Particle Cross-Sectional Image

For the image of a particle cross section is used a reflected electronimage acquired at an acceleration voltage of 10 kV using a scanningelectron microscope (SEM). An SEM observation sample for acquiring aparticle cross-sectional image may be prepared by any method, and aparticle cross-sectional image is acquired using an SEM after a sampleis prepared by cutting an electrode plate containing the carbon materialfor a non-aqueous secondary battery, a film coated with the carbonmaterial for a non-aqueous secondary battery, with a focused ion beam(FIB) or ion milling to obtain a particle cross section.

The acceleration voltage in observing the cross section of the carbonmaterial for a non-aqueous secondary battery with a scanning electronmicroscope (SEM) is 10 kV.

This acceleration voltage makes a difference between a reflectedelectron SEM image and a secondary electron SEM image to allow voidregions and other regions of the carbon material for a non-aqueoussecondary battery to be easily distinguished. The imaging magnificationis typically 500× or more, more preferably 1,000× or more, still morepreferably 2,000× or more, and typically 10,000 or less. An imagingmagnification in this range enables the acquisition of an entire imageof one particle of the carbon material for a non-aqueous secondarybattery. The resolution is 200 dpi (ppi) or more, preferably 256 dpi(ppi) or more. The number of picture elements suitable for evaluation isat least 800 pixels.

Average Box-Counting Dimension Relative to Void Regions inCross-Sectional SEM Image

The carbon material for a non-aqueous secondary battery has an averagebox-counting dimension relative to void regions of 1.55 or greater,preferably 1.60 or greater, more preferably 1.62 or greater, andtypically 1.80 or less, preferably 1.75 or less, more preferably 1.70 orless, as calculated from images obtained by randomly selecting 30granulated particles satisfying (1L) and (2L) above from across-sectional SEM image, dividing the cross-sectional SEM image ofeach granulated particle into void regions and non-void regions, andbinarizing the image.

An excessively small average box-counting dimension relative to voidregions means that the amount of finer structure is small, in which caseexcellent output characteristics, one of the effects of the presentinvention, cannot be provided. An excessively large average box-countingdimension increases the specific surface area of the particles, leadingto low initial efficiency.

The box-counting dimensions of the particles of the carbon material fora non-aqueous secondary battery are determined taking the following (a)to (d) into account.

(a) Definition and Calculation Method of Box-Counting Dimension

Box-counting dimension is a method for estimating a fractal dimension byobserving a certain area split into certain sizes (box sizes) to examinehow much fractal patterns are contained (see, for example, JP 2013-77702A). Box-counting dimension is an indicator of shape complexity, thedegree of surface irregularity, and others, and larger fractaldimensions indicate more complex irregularities. The Box-countingdimension is defined below. The fractal dimension is defined by thefollowing formula, where Nδ (F) is the number of square boxes of side δnecessary for covering a pattern F.

$\begin{matrix}{D = {\lim\limits_{\delta\rightarrow 0}\frac{N_{\delta}(F)}{\log \; \delta}}} & \left\lbrack {{Mathematical}\mspace{14mu} 3} \right\rbrack\end{matrix}$

In this embodiment (e.g., but not limited to, Invention L¹), across-sectional SEM image of a particle composed of voids and carbon issplit into grid areas (boxes) at regular intervals δ (split into squaresubareas of side δ), and the number of boxes containing voids is countedwith varying values of δ. Next, a double logarithmic graph is createdwith the number of boxes counted plotted on the vertical axis and 8 onthe horizontal axis, and a fractal dimension is determined from theslope of the graph.

Specifically, in a cross-sectional SEM image of a particle composed ofvoids and carbon, voids and other regions of the particle are binarized.The binarization is performed in units of pixels of the image. Analysisobjects are portions representing pixels of voids among the binarizedregions. The region outside the particle (outside the outline of theparticle) requires value conversion so as not to be regarded as a void.The image is split into grid areas (boxes) having a specific pixel size.Although the boxes may be arranged in any manner, they are preferablyarranged parallel to the major axis (the longest diameter passingthrough the barycenter) of the particle. In the arrangement, the imageis split into boxes as shown in FIGS. 7 and 8. The number of split boxesincluding at least one pixel representing a void is counted. The sameprocedure is repeated with varying box sizes, and a double logarithmicgraph is created with the number of boxes counted plotted on thevertical axis and the box size δ on the horizontal axis. A linearapproximation of this plot is performed, and the slope of the line ismultiplied by −1. The product obtained is the fractal dimensionaccording to the box-counting method. The slope may be calculated by theleast-squares method.

The fractal dimension is an indicator of the degree of self-similarity,and in expressing a binarized image, it serves as an indicator of thecomplexity and the fineness of a structure. This means that in abinarized image having a more complicated partial structure, theproportion of fine structure in a box tends to increase, that is, theslope tends to be steeper with decreasing box size, and the fineness ofthe partial structure and the amount of such structure are expressed. Inother words, the box-counting dimension in the present invention is anindicator of the complexity of a fine structure of voids and the amountof such structure.

(b) Definition of Box Size

The image may be split into any box size, but based on the maximum pixelof the image, it is preferably split into 10 parts or more, morepreferably 15 parts or more, particularly preferably 20 parts or more,and typically 50 parts or less, preferably 40 parts or less, morepreferably 30 parts or less, on a logarithmic graph. A box size in thisrange reduces the possibility that differences between picture elementsoccur and eliminates the need for a high-resolution image.

(c) Method of Binarization

The binarization may be carried out by any method by whichintra-particle voids and carbon portions are clearly distinguished fromeach other, as shown in FIG. 9. The binarization, when performed on an8-bit gray-scale image, such as an SEM image, refers to dividingluminances into two and representing the two divided images in twovalues (e.g., 0 and 255, in the case of 8-bit). The binarization may becarried out using any desired image processing software. The division bysetting a threshold can be carried out using any algorithm, such as themode method and the Iterative Self-Organizing Data (ISOData) method, bywhich void portions and carbon portions can be clearly distinguishedfrom each other.

The target image needs to be a binarizable image. The binarizable image,in this case, refers to an image in which the luminance of void portionsand the luminance of carbon portions are clearly distinguished from eachother by a certain threshold. In some images, the surface may be roughdue to low processing accuracy; the cross section may be facingobliquely; or the luminances of void portions and carbon portions may beclose to each other depending on the settings such as contrast andbrightness. Such images may show incorrect void distributions whenbinarized and thus are preferably excluded from analysis objects. Forexample, FIG. 10 is an image in which the surface of a graphite portionin the middle has a rough pattern and a low luminance, and fine voidshave high luminances. When such an image is binarized picking up fineparts, carbon portions are also expressed as voids; by contrast, if aluminance at a carbon portion with no void is used as a threshold, finevoids, which are actually voids, cannot be displayed. Although suchparticles are preferably not selected, the cross section of suchparticles may be typical, and thus it is necessary not to analyze suchan SEM image unsuitable for binarization but to retake an image andadjust the brightness and the contrast.

(d) Definition of Particle Boundary

The particle boundary may be established by any method by which theboundary is clearly defined. For example, it may be established byfreehand or the approximation by a polygon. In defining the boundary, itis necessary to establish the boundary between the particle and otherregions such that the region of interest (ROI) representing the shape ofthe particle is completely included. When the boundary is not a simpleoval but has a complicated shape, for example, the boundary may bedivided into any desired number of equally spaced sections toapproximate the particle region by a polygon. The boundary, however, isestablished so as not to deviate from a roundness R determined with aflow-type particle image analyzer. As used herein, “not deviate” meansthat a degree of spheroidization R determined by a flow-type particleimage analyzer and a degree of spheroidization R₁ determined from across-sectional SEM image satisfy the relationship |R−R₁|≦0.1. When anelectrode coated with a binder having poor conductivity is used, theboundary may be difficult to determine under the measurement conditionsin this embodiment. This is probably a phenomenon that occurs due to thepoor conductivity of the binder when the side of the particle is visiblein depth of the cross section of the particle. In such a case, it isnecessary to take an image with a clear boundary at a lower accelerationvoltage to determine a boundary.

In one aspect of one embodiment of the present invention, the carbonmaterial for a non-aqueous secondary battery is a carbon material for anon-aqueous secondary battery comprising uniformly dispersedintra-particle pores.

Specifically, the carbon material for a non-aqueous secondary batteryaccording to an embodiment of the present invention (e.g., but notlimited to, Invention L²) comprises a carbon material made of granulatedparticles satisfying (1L) and (2L) above and further has acharacteristic particle cross section such that the void dispersity D ofthe present invention is determined from an image of the particle crosssection.

Void Dispersity D in Cross-Sectional SEM Image

The carbon material for a non-aqueous secondary battery typically has anaverage dispersity D of 30 particles, as determined by the followingmeasurement method using 30 granulated particles satisfying (1L) and(2L) above randomly selected from a cross-sectional SEM image, of 60% ormore, preferably 61% or more, more preferably 62% or more, and typically90% or less, preferably 85% or less, more preferably 80% or less.

Measurement Method

Using a cross-sectional SEM image, grid lines are drawn to split theminor axis and the major axis of a target granulated particle each into20 parts. Using cells in the grid, the granulated particle iscompartmentalized as defined below. The expectation E of void area ofeach compartment is calculated using equation (A) below, and thedispersity D of the granulated particle is calculated using equation (B)below.

The cross-sectional SEM image is a reflected electron image acquired atan acceleration voltage of 10 kV.

How to Create Grid

Using a cross-sectional SEM image, grid lines are drawn to split theminor axis and the major axis of a target granulated particle each into20 parts, as shown in FIG. 11. This image needs to be parallel to theparticle major axis and the image.

Definition of Compartment

The compartment is defined as a granulated particle portion and/or aregion where a void is present in the granulated particle in each cellof the grid. The outside of the boundary of the granulated particle isexcluded from the compartment. For grid cells that are divided by theparticle boundary into two, as shown in FIG. 12, the region includingthe particle is defined as a compartment.

Definition of Expectation

For compartments defined by grid lines and the particle boundary, theexpectation E of a void area corresponding to each compartment area isdetermined from equation (A).

Expectation E [μm²] of void area in target compartment=(gross area [μm²]of internal voids of one target granulated particle)/(cross-sectionalarea [μm²] of one target granulated particle)×(area [μm²] of targetcompartment)  Equation (A)

The expectation E of a compartment defined by the particle boundary iscalculated to be smaller than the expectation E of a grid cell accordingto the area of the compartment.

Definition of Dispersity D

The dispersity D, an indicator of the void dispersity in a particle, iscalculated by equation (B).

Dispersity D (%)=(sum total [μm²] of areas of compartments that satisfy(gross area [μm²] of voids in target compartment)/(expectation E [μm²]of void area in target compartment)=0.5 or greater)/(sum total [μm²] ofareas of all the compartments of one target granulatedparticle)×100  Equation (B)

The dispersity D indicates how voids are dispersed throughout the insideof a particle, excluding compartments having only a small void area.

The equation (A) and the equation (B) of the carbon material for anon-aqueous secondary battery are calculated taking the following (a) to(d) into account.

(a) Method of Selecting Granulated Particles and Definition of MajorAxis and Minor Axis

The particle boundary may be established by any method by which theboundary is clearly defined. For example, it may be established byfreehand or the approximation by a polygon. In defining the boundary, itis necessary to establish the boundary between the particle and otherregions such that the region of interest (ROI) representing the shape ofthe particle is completely included. When the boundary is not a simpleoval but has a complicated shape, for example, the boundary may bedivided into any desired number of equally spaced sections toapproximate the particle region by a polygon. The boundary, however, isestablished so as not to deviate from a roundness R determined with aflow-type particle image analyzer. As used herein, “not deviate” meansthat a degree of spheroidization R determined by a flow-type particleimage analyzer and a degree of spheroidization R₁ determined from across-sectional SEM image satisfy the relationship |R−R₁|≦0.1. When anelectrode coated with a binder having poor conductivity is used, theboundary may be difficult to determine under the measurement conditionsin this embodiment. This is probably a phenomenon that occurs due to thepoor conductivity of the binder when the side of the particle is visiblein depth of the cross section of the particle. In such a case, it isnecessary to retake an image with a clear boundary at a loweracceleration voltage to determine a boundary.

For one randomly selected granulated particle, the barycenter (centroid)is defined. First, the particle defined by the boundary is approximatedby square cells. The size of each cell is preferably, but notnecessarily, 5 nm or less in actual size. Two-dimensional coordinatesare determined in the image. The coordinates of the barycenter of eachcell are defined. Assuming that the weights of the cells are the same,the cells are numbered from 1 to N. The following formula is used todetermine the coordinates of the barycenter of the granulated particle.

$\begin{matrix}{\overset{\rightarrow}{r_{G}} = \frac{{\Sigma_{1}^{N}}_{\overset{\rightarrow}{r_{i}}}}{N}} & \left\lbrack {{Mathematical}\mspace{14mu} 4} \right\rbrack\end{matrix}$

In the formula, r_(i) represents the coordinates of an i-th cell, andr_(G) represents the coordinates of the barycenter. The barycenter maybe determined by operating any desired image software, or by thefollowing formula if the barycenter of each divided mesh can be definedby any given figure.

$\begin{matrix}{\overset{\rightarrow}{r_{G}} = \frac{\sum_{1}^{N}{A_{i}\overset{\rightarrow}{r_{i}}}}{\sum_{1}^{N}A_{i}}} & \left\lbrack {{Mathematical}\mspace{14mu} 5} \right\rbrack\end{matrix}$

In the formula, A_(i) is the area of an i-th figure, and r_(i) is thebarycentric (centroid) coordinates of the i-th figure.

Next, the longest line segment among line segments passing through thebarycenter obtained and bounded by the boundary fixed as described aboveis defined as a major axis. The line segment orthogonal to the majoraxis among line segments passing through the barycenter and bounded bythe boundary fixed as described above is defined as a minor axis.

(b) Definition of Void Region and Non-Void Region and Method ofCalculating their Areas

The binarization may be carried out by any method by whichintra-particle voids and carbon portions are clearly distinguished fromeach other, as shown in FIG. 9, and is preferably carried out such thatvoid regions and other carbon particle regions are clearly distinguishedfrom each other. The binarization, when performed on an 8-bit gray-scaleimage, such as an SEM image, refers to dividing luminances into two andrepresenting the two divided images in two values (e.g., 0 and 255, inthe case of 8-bit). The binarization may be carried out using anydesired image processing software. The division by setting a thresholdcan be carried out using any algorithm, such as the mode method and theISOData method, by which void portions and carbon portions can beclearly distinguished from each other. The target image needs to be abinarizable image. The binarizable image refers to an image in which theluminance of void portions and the luminance of carbon portions areclearly distinguished from each other by a certain threshold. In someimages, the surface may be rough due to low processing accuracy; thecross section may be facing obliquely; or the luminances of voidportions and carbon portions may be close to each other depending on thesettings such as contrast and brightness. Such images may show incorrectvoid distributions when binarized and thus are preferably excluded fromanalysis objects. For example, FIG. 10 is an image in which the surfaceof a graphite portion in the middle has a rough pattern and a lowluminance, and fine voids have high luminances. When such an image isbinarized picking up fine parts, carbon portions are also expressed asvoids; by contrast, if a luminance at a carbon portion with no void isused as a threshold, fine voids, which are actually voids, cannot bedisplayed. Although such particles are preferably not selected, thecross section of such particles may be typical, and thus it is necessarynot to analyze such an SEM image unsuitable for binarization but toretake an image and adjust the brightness and the contrast.

The areas of the void region and the non-void region in the particlethus calculated are each calculated as an approximation in a pixel unitand converted into an actual unit.

(c) Creation of Grid

In the binarized image is created cells that split the minor axis andthe major axis of the granulated particle each into 20 parts. As for thecell arrangement, the cells may be arranged such that they are parallelto the major axis and the minor axis of the granulated particle.

(d) Calculation of Expectation E and Dispersity D of Target Compartment

For each of the 400 cells created by splitting the minor axis and themajor axis of the granulated particle each into 20 parts, theexpectation E is calculated by equation (A) above. The sum total ofareas of compartments having an expectation E of 0.5 or greater iscalculated, and the dispersity D is calculated by equation (B) above.

For each of the 30 granulated particles selected, the dispersity D iscalculated, and the average dispersity D of the 30 particles iscalculated.

In one aspect of one embodiment of the present invention, the carbonmaterial for a non-aqueous secondary battery is preferably a carbonmaterial for a non-aqueous secondary battery comprising intra-particlevoids the orientation of which and the interval between which arecontrolled.

Specifically, the carbon material for a non-aqueous secondary batteryaccording to an embodiment of the present invention (e.g., but notlimited to, Invention L³) comprises a carbon material made of granulatedparticles satisfying the following (1L) and (2L) and further has acharacteristic particle cross section such that the ratio (Zave/X) ofaverage inter-void distance Z (Zave) of 30 particles to volume-basedaverage particle diameter X determined by laser diffraction of thepresent invention is determined from an image of the particle crosssection.

Zave/X

The carbon material for a non-aqueous secondary battery according tothis embodiment (e.g., but not limited to, Invention L³) comprisesgranulated particles satisfying (1L) and (2L) above and has an averageinter-void distance Z (Zave) of 30 particles as defined below and avolume-based average particle diameter X determined by laser diffractionin a ratio (Zave/X) of typically 0.060 or less, preferably 0.055 orless, more preferably 0.050 or less, still more preferably 0.045 orless, and typically 0.001 or greater, preferably 0.010 or greater, morepreferably 0.020 or greater, the 30 granulated particles satisfying (1L)and (2L) above and being randomly selected from a cross-sectional SEMimage.

An excessively large Zave/X means that the distance between the carbonmaterial and voids constituting the granulated particle is wide, whichresults in a low liquid retention in the particle.

Definition of Average Inter-Void Distance Z (Zave) of 30 Particles

As shown in the left figure of FIG. 13, three lines are drawn that areparallel to the minor axis of a target granulated particle and split themajor axis of the granulated particle into four parts, and inter-voiddistances Z (μm) of the granulated particle on each line (see the rightfigure of FIG. 13) are each measured. The average of 30 particles intotal is calculated. This is defined as the average inter-void distanceZ (Zave) of 30 particles.

W/X

In this embodiment (e.g., but not limited to, Invention L³), the carbonmaterial for a non-aqueous secondary battery comprises granulatedparticles satisfying (1L) and (2L) above and has a standard deviation(W) of void sizes Y of 30 particles as defined below and a volume-basedaverage particle diameter X determined by laser diffraction in a ratio(W/X) of preferably 0.018 or less, more preferably 0.016 or less, stillmore preferably 0.014 or less, and typically 0.001 or greater,preferably 0.005 or greater, more preferably 0.008 or greater, the 30granulated particles satisfying (1L) and (2L) above and being randomlyselected from a cross-sectional SEM image.

W/X is a quotient of a standard deviation of void sizes divided by aparticle size, and a larger value of W/X means that a higher proportionof relatively large voids.

A W/X in the above range means relatively uniform void sizes or a lowproportion of large voids, meaning that the carbon material has a finevoid structure that allows an electrolyte solution to uniformly permeateinto the particles.

Definition of Standard Deviation (W) of Void Sizes Y (μm) of 30Particles

As shown in the left figure of FIG. 13, three lines are drawn that areparallel to the minor axis of a target granulated particle and split themajor axis of the granulated particle into four parts, and void sizes Y(μm) of the granulated particle on each line (see the right figure ofFIG. 13) are each measured. The standard deviation of 30 particles intotal is calculated. This is defined as the standard deviation (W) ofvoid sizes Y of 30 particles.

The standard deviation is determined by the following formula, whereYave is the average of Y, and Ny is the number of Y.

$\begin{matrix}{W = \left( \frac{\sum\left( {Y - Y_{ave}} \right)^{2}}{Ny} \right)^{1/2}} & \left\lbrack {{Mathematical}\mspace{14mu} 6} \right\rbrack\end{matrix}$

Condition of Voids

Preferably, the granulated particles in the carbon material for anon-aqueous secondary battery according to this embodiment (e.g., butnot limited to, Invention L³) have slit-like voids, and the slit-likevoids are arranged mainly in layers.

More specifically, among 30 granulated particles satisfying (1L) and(2L) above randomly selected from a cross-sectional SEM image, theproportion (by number) of particles having slit-like voids arrangedmainly in layers is more preferably 70% or more, particularly preferably80% or more, most preferably 90% or more. Within this range, it can besaid that most of all the particles have voids having a slit-like andlayered structure.

“Slit-like void” refers to a long and narrow void (with a high aspectratio) like a gap. The aspect ratio of the void is preferably 10 orgreater, more preferably 15 or greater. The aspect ratio is a valueobtained by dividing the major axis of the void by the minor axis, thatis, (major axis of void)/(minor axis of void). The major axis and theminor axis of the void can be calculated by the same method as inSelection of Granulated Particles and Definition of Minor Axis describedbelow.

“Voids in layers” means that major axes of voids in a particle arearranged in parallel. If the angle between the major axes of two voidsis within ±30°, the two voids are regarded as being in parallel.

The proportion of the area of voids in layers (the area of voids inlayers/the gross area of voids) in a granulated particle is preferably40% or more, more preferably 50% or more, still more preferably 60% ormore, and typically 100% or less, preferably 90% or less. The proportionof the number of slit-like voids (the number of slit-like voids/thetotal number of voids) is preferably 70% or more, more preferably 80% ormore, still more preferably 90% or more, and typically 100% or less,preferably 90% or less. If the number and the area of slit-like voidsare in these ranges, it can be said that the particle has so many fineslit-like structures that provide more reaction initiation surfaces ofLi and sufficient permeability of electrolyte solution.

The above-described Zave/X and W/X of the carbon material for anon-aqueous secondary battery are calculated taking the following (a) to(d) into account.

(a) Selection of Granulated Particles and Definition of Minor Axis

In an SEM image acquired, 30 granulated particles satisfying the aboveconditions (1L) and (2L) are randomly selected. In the selection,particle boundaries are established along the outlines of the granulatedparticles. The particle boundary may be established by any method bywhich the boundary is clearly defined, that is, the boundary between theparticle and other regions is established such that the region ofinterest (ROI) representing the shape of the particle is completelyincluded. For example, it may be established by freehand or theapproximation by a polygon. When the boundary is not linear-like but hasa complicated shape, for example, the boundary may be divided into anydesired number of equally spaced sections to approximate the particleregion by a polygon. The boundary is established so as not to deviatefrom a roundness R determined with a flow-type particle image analyzer.As used herein, “not deviate” means that a degree of spheroidization Rdetermined by a flow-type particle image analyzer and a degree ofspheroidization R₁ determined from a cross-sectional SEM image satisfythe relationship |R−R₁|≦0.1.

For one randomly selected granulated particle, the barycenter (centroid)is defined. First, the particle defined by the boundary is approximatedby square cells. The size of each cell is preferably, but notnecessarily, 5 nm or less in actual size. Two-dimensional coordinatesare determined in the image. The coordinates of the barycenter of eachcell are defined. Assuming that the weights of the cells are the same,the cells are numbered from 1 to N. The following formula is used todetermine the coordinates of the barycenter of the granulated particle.

$\begin{matrix}{\overset{\rightarrow}{r_{G}} = \frac{\sum_{1}^{N}\overset{\rightarrow}{r_{i}}}{N}} & \left\lbrack {{Mathematical}\mspace{14mu} 7} \right\rbrack\end{matrix}$

In the formula, r_(i) represents the coordinates of an i-th cell, andr_(G) represents the coordinates of the barycenter. The barycenter maybe determined by operating any desired image software, or by thefollowing formula if the barycenter of each divided mesh can be definedby any given figure.

$\begin{matrix}{\overset{\rightarrow}{r_{G}} = \frac{\sum_{1}^{N}{A_{i}\overset{\rightarrow}{r_{i}}}}{\sum_{1}^{N}A_{i}}} & \left\lbrack {{Mathematical}\mspace{14mu} 8} \right\rbrack\end{matrix}$

In the formula, A_(i) is the area of an i-th figure, and r_(i) is thebarycentric (centroid) coordinates of the i-th figure.

Next, the longest line segment among line segments passing through thebarycenter obtained and bounded by the boundary fixed as described aboveis defined as a major axis. The line segment orthogonal to the majoraxis among line segments passing through the barycenter and bounded bythe boundary fixed as described above is defined as a minor axis.

(b) Definition and Calculation Method of Intra-Particle Voids

If necessary, binarization may be performed such that void regions andother carbon particle regions are clearly distinguished from each other.As shown in FIG. 9, the binarization may be carried out by any method bywhich intra-particle voids and carbon portions are clearly distinguishedfrom each other. It is supposed that the image to be processed is an8-bit gray-scale image, the luminance of one picture element (1 Pixel)of which is expressed by a natural number from 0 to 255. Thebinarization refers dividing luminances into two and representing thetwo divided images in two values (e.g., 0 and 255 in this case). Thebinarization may be carried out using any desired image processingsoftware. The division by setting a threshold can be carried out usingany algorithm, such as the mode method and the ISOData method, by whichvoid portions and carbon portions can be clearly distinguished from eachother. The target image needs to be a binarizable image. The binarizableimage, in this case, refers to an image in which the luminance of voidportions and the luminance of carbon portions are clearly distinguishedfrom each other by a certain threshold. In some images, the surface maybe rough due to low processing accuracy; the cross section may be facingobliquely; or the luminances of void portions and carbon portions may beclose to each other depending on the settings such as contrast andbrightness. Such images may show incorrect void distributions whenbinarized and thus are preferably excluded from analysis objects. Forexample, FIG. 10 is an image in which the surface of a graphite portionin the middle has a rough pattern and a low luminance, and fine voidshave high luminances. When such an image is binarized picking up fineparts, carbon portions are also expressed as voids; by contrast, if aluminance at a carbon portion with no void is used as a threshold, finevoids, which are actually voids, cannot be displayed. Although suchparticles are preferably not selected, the cross section of suchparticles may be typical, and thus it is necessary not to analyze suchan SEM image unsuitable for binarization but to retake an image andadjust the brightness and the contrast.

(c) Voids on Line of Granulated Particle

“Voids in a granulated particle intersecting the minor axis of thegranulated particle” refers to voids on three lines that are parallel tothe minor axis of the granulated particle and split the major axis ofthe granulated particle into four parts (see FIG. 13). Picture elementsintersecting lines translated from the three lines parallel to the minoraxis of the granulated particle in the major axis direction by ±0.5pixel are regarded as voids on the minor axis.

(d) Average Interval (Zave) Between Voids and Standard Deviation (W) ofVoid Sizes

The interval between voids (the distance between a void and a void) inone randomly selected granulated particle is determined on theabove-described three lines parallel to the minor axis of the granulatedparticle (see FIG. 13). In one granulated particle, distances Z betweenvoids on the three lines parallel to the minor axis are each measured.This measurement is made on 30 particles. Its average value is definedas the average inter-void distance Z (Zave) of 30 particles.

Furthermore, sizes Y of voids on the three lines (see FIG. 13) are eachmeasured. This measurement is made on 30 particles. Its standarddeviation is defined as the standard deviation (W) of void sizes Y of 30particles.

In this embodiment (e.g., but not limited to, Invention L³), voids inthe granulated particle are preferably arranged, mainly, relativelyparallel to the major axis of the granulated particle.

Physical Properties of Composite Carbon Material for Non-AqueousSecondary Battery

A description will be given below of preferred physical properties ofthe composite carbon material. Physical properties not described in thissection are preferably within the ranges of the physical properties ofthe carbon material for a non-aqueous secondary battery described above.

Volume-Based Average Particle Diameter (Average Particle Diameter d50)

The volume-based average particle diameter (also referred to as “averageparticle diameter d50”) of the composite carbon material is preferably 1μm or more, more preferably 5 μm or more, still more preferably 8 μm ormore, particularly preferably 10 μm or more, most preferably 11 μm ormore. The average particle diameter d50 is preferably 50 μm or less,more preferably 40 μm or less, still more preferably 35 μm or less, evenmore preferably 31 μm or less, particularly preferably 30 μm or less,most preferably 25 μm or less. An average particle diameter in thisrange tends to prevent the increase in irreversible capacity and preventstreaks that can occur during a slurry application, thus leading to noreduction in productivity. In other words, an excessively small averageparticle diameter d50 tends to cause an increase in irreversiblecapacity and a loss in initial battery capacity of a non-aqueoussecondary battery comprising the composite carbon material, and anexcessively large average particle diameter d50 can cause processdefects such as streaks that occur in a slurry application, degradedhigh-current-density charge-discharge characteristics, and degradedlow-temperature output characteristics.

The average particle diameter d50 is defined as a volume-based mediandiameter determined by suspending 0.01 g of a composite carbon materialin 10 mL of a 0.2% by mass aqueous solution of a polyoxyethylenesorbitan monolaurate surfactant (e.g., Tween 20 (registered trademark)),placing the suspension (a measurement sample) in a commerciallyavailable laser diffraction/scattering particle size distributionanalyzer (e.g., LA-920 available from HORIBA), irradiating themeasurement sample with ultrasonic waves of 28 kHz at a power of 60 Wfor 1 minute, and then performing a measurement with the analyzer.

Tap Density

The tap density of the composite carbon material is typically in therange of 0.6 g/cm³ or more, preferably 0.70 g/cm³ or more, morepreferably 0.75 g/cm³ or more, still more preferably 0.8 g/cm³ or more,even more preferably 0.85 g/cm³ or more, particularly preferably 0.88g/cm³ or more, more particularly preferably 0.9 g/cm³ or more, mostpreferably 0.93 g/cm³ or more, and typically 1.5 g/cm³ or less,preferably 1.3 g/cm³ or less, more preferably 1.2 g/cm³ or less, stillmore preferably 1.1 g/cm³ or less.

A tap density in this range prevents streaks that can occur during theformation of an electrode plate, thus leading to improved productivityand excellent fast charge-discharge characteristics. In addition, such atap density tends to inhibit the increase in intraparticle carbondensity, thus providing good rolling properties and making it easy toform a high-density negative electrode sheet.

The tap density is defined as a density calculated from a volume and amass of a sample. The volume is determined as follows: using a powderdensity meter, the composite carbon material particles are droppedthrough a sieve with openings of 300 μm into a cylindrical tap cell witha diameter of 1.6 cm and a volume capacity of 20 cm³ to fill up thecell; a tap with a stroke length of 10 mm is given 1,000 times; and thevolume at this time is measured.

Roundness

The roundness of the composite carbon material is 0.88 or greater,preferably 0.90 or greater, more preferably 0.91 or greater. Theroundness is preferably 1 or less, more preferably 0.98 or less, stillmore preferably 0.97 or less. A roundness in this range tends to inhibitthe degradation of high-current-density charge-discharge characteristicsof non-aqueous secondary batteries. The roundness is defined by thefollowing equation, and a theoretically perfect sphere has a roundnessof 1.

A roundness in the above range tends to decrease the degree of flectionof Li-ion diffusivity to smoothen the movement of electrolyte solutionin intra-particle voids and enable moderate contact between thecomposite particles, thus providing good fast charge-dischargecharacteristics and cycle characteristics.

Roundness=(perimeter of equivalent circle having the same area asprojected particle shape)/(actual perimeter of projected particle shape)

As the value of the roundness is used a value determined, for example,using a flow-type particle image analyzer (e.g., FPIA available fromSysmex Industrial Corp.) by dispersing about 0.2 g of a sample(composite particles) in a 0.2% by mass aqueous solution (approximately50 mL) of a polyoxyethylene (20) sorbitan monolaurate surfactant,irradiating the dispersion with ultrasonic waves of 28 kHz at a power of60 W for 1 minute, and then measuring the roundness of particles with adiameter in the range of 1.5 to 40 μm with a detection range set to 0.6to 400 μm.

X-Ray Parameter

The d-value (interplanar spacing) of lattice planes ((002) planes) ofthe composite carbon material, as determined by X-ray diffractometry inaccordance with the method of the Japan Society for Promotion ofScientific Research, is preferably 0.335 nm to less than 0.340 nm. Thed-value is more preferably 0.339 nm or less, still more preferably 0.337nm or less. A d₀₀₂-value in this range tends to increase thecrystallinity of the graphite, thus inhibiting the increase in initialirreversible capacity. The theoretical value of graphite is 0.335 nm.

The crystallite size (Lc) of the composite particles, as determined byX-ray diffractometry in accordance with the method of the Japan Societyfor Promotion of Scientific Research, is preferably in the range of 90nm or more, more preferably 100 nm or more. A crystallite size in thisrange provides particles having not too low crystallinity, thusproviding a non-aqueous secondary battery the reversible capacity ofwhich is less likely to decrease.

Ash Content

The ash content of the composite carbon material is preferably 1% bymass or less, more preferably 0.5 W by mass or less, still morepreferably 0.1% by mass or less, based on the total mass of thecomposite carbon material. The ash content is preferably at least 1 ppm.

An ash content in this range can provide a non-aqueous secondary batterythat undergoes only negligible degradation of battery performance due tothe reaction between composite particles and electrolyte solution duringcharging and discharging. In addition, such an ash content does notrequire much time or energy to produce a carbon material and eliminatesthe need for equipment for preventing contamination, thus reducing theincrease in cost.

BET Specific Surface Area (SA)

The specific surface area (SA) of the composite carbon material, asdetermined by BET method, is preferably 1 m²/g or more, more preferably2 m²/g or more, still more preferably 3 m²/g or more, particularlypreferably 4 m²/g or more, and preferably 30 m²/g or less, morepreferably 20 m²/g or less, still more preferably 17 m²/g or less,particularly preferably 15 m²/g or less, most preferably 12 m²/g orless.

A specific surface area in this range tends to sufficiently secure siteswhere Li enters and exits, thus providing excellent fastcharge-discharge characteristics and output characteristics, and tendsto moderately control the activity of the composite carbon material, anactive material, against electrolyte solution, thus inhibiting theincrease in initial irreversible capacity, as a result of which ahigh-capacity battery can be produced.

Furthermore, such a specific surface area can inhibit the increase inthe reactivity of a negative electrode formed using the composite carbonmaterial with an electrolyte solution to reduce gas generation, thusproviding a preferred non-aqueous secondary battery.

The BET specific surface area is defined as a value determined asfollows: using a surface area meter (e.g., a Gemini 2360 specificsurface area analyzer available from Shimadzu Corporation), a compositeparticle sample is preliminarily vacuum dried under a nitrogen stream at100° C. for 3 hours and then cooled to liquid nitrogen temperature, andusing a nitrogen-helium mixed gas precisely regulated so as to have anitrogen pressure of 0.3 relative to atmospheric pressure, a BETspecific surface area is measured by a nitrogen adsorption BETmultipoint method according to a flowing gas method.

True Density

The true density of the composite carbon material is preferably 1.9g/cm³ or more, more preferably 2 g/cm³ or more, still more preferably2.1 g/cm³ or more, particularly preferably 2.2 g/cm³ or more, and up to2.26 g/cm³. The upper limit is the theoretical value of graphite. A truedensity in this range tends to avoid too low carbon crystallinity, thusinhibiting the increase in initial irreversible capacity of non-aqueoussecondary batteries.

Aspect Ratio

The aspect ratio of the composite carbon material in powder form istheoretically 1 or greater, preferably 1.1 or greater, more preferably1.2 or greater. The aspect ratio is preferably 10 or less, morepreferably 8 or less, still more preferably 5 or less.

An aspect ratio in this range tends to prevent streaks of a slurry (amaterial for forming a negative electrode) containing the compositeparticles from occurring during the formation of an electrode plate soas to provide a uniform coated surface, thus avoiding degradedhigh-current-density charge-discharge characteristics of non-aqueoussecondary batteries.

The aspect ratio is expressed as A/B, where A is the longest diameter ofa composite particle observed in a three-dimensional manner, and B isthe shortest diameter among the diameters orthogonal to the longestdiameter. The observation of the composite particle is carried out undera scanning electron microscope capable of magnifying observation. Fiftycomposite particles immobilized on the surface of a metal having athickness of 50 microns or less are randomly selected. For each of theparticles, A and B are determined while a stage on which the samples areimmobilized is rotated and tilted, and the average value of A/B iscalculated.

Raman R Value

The Raman R value of the composite carbon material is preferably 0.01 orgreater, more preferably 0.1 or greater, still more preferably 0.15 orgreater, particularly preferably 0.2 or greater. The Raman R value istypically 1 or less, preferably 0.6 or less, more preferably 0.5 orless, still more preferably 0.4 or less.

The Raman R value is defined as an intensity ratio (I_(B)/I_(A)) in aRaman spectrum obtained by Raman spectroscopy, where I_(A) is anintensity of peak P_(A) near 1,580 cm⁻¹, and I_(B) is an intensity ofpeak P_(B) near 1,360 cm¹.

As used herein, “near 1,580 cm⁻¹” refers to a range of 1,580 to 1,620cm⁻¹, and “near 1,360 cm⁻¹” a range of 1,350 to 1,370 cm⁻¹.

A Raman R value in this range tends to reduce the possibility that thecrystallinity of the surface of the composite carbon material increasesand that crystals, when the density is increased, are oriented in thedirection parallel to a negative electrode plate, thus avoiding degradedload characteristics. Furthermore, such a Raman R value tends to reducethe possibility that crystals on the particle surface of the compositecarbon material are disordered and inhibit the increase in thereactivity of a negative electrode with an electrolyte solution, thusavoiding reduced charge-discharge efficiency and increased gasgeneration of non-aqueous secondary batteries.

The Raman spectrum described above can be measured using a Ramanspectroscope. Specifically, a sample is loaded by gravity-droppingtarget particles into a measuring cell, and the measuring cell isirradiated with an argon-ion laser beam while being rotated in a planeperpendicular to the laser beam. The measurement conditions are asfollows:

Wavelength of argon-ion laser beam: 514.5 nm

Laser power on sample: 25 mW

Resolution: 4 cm⁻¹

Measurement range: 1,100 cm⁻¹ to 1,730 cm⁻¹

Measurement of peak intensity, measurement of peak half-width:background processing, smoothing processing (convolution by simpleaverage, 5 points)

Mode Pore Diameter (PD) in Pore Diameter Range of 0.01 μm to 1 μm

The mode pore diameter (PD) in a pore diameter range of 0.01 μm to 1 μmof the composite carbon material is a value determined by mercuryintrusion (mercury porosimetry) and typically 0.01 μm or more,preferably 0.03 μm or more, more preferably 0.05 μm or more, still morepreferably 0.06 μm or more, particularly preferably 0.07 μm or more, andtypically 1 μm or less, preferably 0.65 μm or less, more preferably 0.5μm or less, still more preferably 0.4 μm or less, even more preferably0.3 μm or less, particularly preferably 0.2 μm or less, most preferably0.1 μm or less.

A mode pore diameter (PD) in a pore diameter range of 0.01 μm to 1 μmoutside this range tends to prevent an electrolyte solution from beingefficiently distributed into intra-particle voids and prevent theefficient use of Li-ion insertion/extraction sites in the particles,thus resulting in degraded low-temperature output characteristics andcycle characteristics.

Cumulative Pore Volume at Pore Diameters in Range of 0.01 μm to 1 μm

The cumulative pore volume at pore diameters in a range of 0.01 μm to 1μm of the composite carbon material is a value determined by mercuryintrusion (mercury porosimetry) and, even when pressure is applied,typically 0.07 mL/g or more, preferably 0.08 mL/g or more, morepreferably 0.09 mL/g or more, most preferably 0.10 mL/g or more, andpreferably 0.3 mL/g or less, more preferably 0.25 mL/g or less, stillmore preferably 0.2 mL/g or less, particularly preferably 0.18 mL/g orless.

An excessively small cumulative pore volume at pore diameters in a rangeof 0.01 μm to 1 μm tends to prevent an electrolyte solution frompermeating into the particles and prevent the efficient use of Li-ioninsertion/extraction sites in the particles. This impedes smoothinsertion/extraction of lithium ions in fast charging and dischargingand results in degraded low-temperature output characteristics. Acumulative pore volume within the above range tends to allow anelectrolyte solution to be smoothly and efficiently distributed into theparticles, thus enabling the effective and efficient use of Li-ioninsertion/extraction sites in the particles as well as on the peripheryof the particles during charging and discharging and providing goodlow-temperature output characteristics.

Half Width at Half Maximum of Pore Distribution (log (nm))

The half width at half maximum of pore distribution (log (nm)) of thecomposite carbon material refers to a half width at half maximum at amicropore side of a peak in a pore diameter range of 0.01 μm to 1 μm ina pore distribution (nm), as determined by mercury intrusion (mercuryporosimetry), with a horizontal axis expressed in common logarithm (log(nm)).

(In the Case where the Composite Carbon Material has a d50 of 13 μm orMore)

The half width at half maximum of pore distribution (log (nm)) of thecomposite carbon material having a d50 of 13 μm or more is preferably0.3 or greater, more preferably 0.35 or greater, still more preferably0.4 or greater, particularly preferably 0.45 or greater, preferably 10or less, more preferably 5 or less, still more preferably 3 or less,particularly preferably 1 or less.

(In the Case where the Composite Carbon Material has a d50 of Less than13 μm)

When the d50 of the composite carbon material is less than 13 μm, itshalf width at half maximum of pore distribution (log (nm)) is preferably0.01 or greater, more preferably 0.05 or greater, still more preferably0.1 or greater, and preferably 0.33 or less, more preferably 0.3 orless, still more preferably 0.25 or less, particularly preferably 0.23or less.

When the half width at half maximum of pore distribution (log (nm)) isin this range, intra-particle voids in a pore diameter range of 0.01 μmto 1 μm tend to be formed to have a finer structure and thus allow anelectrolyte solution to be smoothly and efficiently distributed into theparticles. This enables the effective and efficient use of Li-ioninsertion/extraction sites in the particles as well as on the peripheryof the particles during charging and discharging, thus providing goodlow-temperature output characteristics and cycle characteristics.

Total Pore Volume

The total pore volume of the composite carbon material is a valuedetermined by mercury intrusion (mercury porosimetry) and preferably 0.1mL/g or more, more preferably 0.3 mL/g or more, still more preferably0.5 mL/g or more, particularly preferably 0.6 mL/g or more, mostpreferably 0.7 mL/g or more, and preferably 10 mL/g or less, morepreferably 5 mL/g or less, still more preferably 2 mL/g or less,particularly preferably 1 mL/g or less.

A total pore volume in this range eliminates the need for using anexcess amount of binder in forming an electrode plate and facilitatesthe diffusion of a thickener and a binder in forming an electrode plate.

As an apparatus for the mercury porosimetry, a mercury porosimeter(Autopore 9520 available from Micromeritics Corp.) can be used. A sample(carbon material) is weighed to around 0.2 g and placed in a powdercell. The cell is sealed, and a pretreatment is carried out by degassingthe cell at room temperature under vacuum (50 μmHg or lower) for 10minutes.

Subsequently, mercury is introduced into the cell under a reducedpressure of 4 psia (approximately 28 kPa). The pressure is increasedstepwise from 4 psia (approximately 28 kPa) to 40,000 psia(approximately 280 MPa) and then reduced to 25 psia (approximately 170kPa).

The number of steps in the pressure increase is at least 80. In eachstep, the amount of mercury intrusion is measured after an equilibrationtime of 10 seconds. From the mercury intrusion curve thus obtained, apore distribution is calculated using the Washburn equation.

The calculation is made assuming that the surface tension (γ) of mercuryis 485 dyne/cm, and the contact angle (Ψ) is 140°. The average porediameter is defined as a pore diameter at a cumulative pore volume of50%.

Ratio (PD/d50(%)) of Mode Pore Diameter (PD) in Pore Diameter Range of0.01 μm to 1 μm to Volume-Based Average Particle Diameter (d50)

The ratio (PD/d50) of mode pore diameter (PD) in a pore diameter rangeof 0.01 μm to 1 μm to volume-based average particle diameter (d50) ofthe composite carbon material is expressed by equation (1A) andtypically 1.8 or less, preferably 1.80 or less, more preferably 1.00 orless, still more preferably 0.90 or less, particularly preferably 0.80or less, most preferably 0.70 or less, and typically 0.01 or greater,preferably 0.10 or greater, more preferably 0.20 or greater.

PD/d50(%)=mode pore diameter (PD) in a pore diameter range of 0.01 μm to1 μm in a pore distribution determined by mercury intrusion/volume-basedaverage particle diameter (d50)×100  Equation (1A):

A mode pore diameter (PD) in a pore diameter range of 0.01 μm to 1 μmoutside this range tends to prevent an electrolyte solution from beingefficiently distributed into intra-particle voids and prevent theefficient use of Li-ion insertion/extraction sites in the particles,thus resulting in degraded low-temperature output characteristics andcycle characteristics.

In one aspect of the composite carbon material according to oneembodiment of the present invention, the relationship of inequality (1D)is satisfied.

Inequality (1D)

10Y _(d)+0.26X _(d)≧α  (1D)

(Y_(d)=tap density (g/cm³), X_(d)=specific surface area (SA) (m²/g) ofcarbon material determined by BET method, α=12.60)

In the composite carbon material according to this embodiment (e.g., butnot limited to, Invention D), a given by inequality (1D) is 12.60 orgreater, preferably 12.65, more preferably 12.70, more preferably 12.80,particularly preferably 13.00.

If the relationship represented by inequality (1D) is not satisfied, thebalance between usable regions in Li-ion insertion/extraction sites inthe particles and particle-filling properties tends to be poor, thusresulting in degraded low-temperature output characteristics and areduced capacity.

The tap density of the composite carbon material according to thisembodiment is preferably 1.00 g/cm³ or more, more preferably 1.05 g/cm³or more, still more preferably 1.10 g/cm³ or more, particularlypreferably 1.12 g/cm³ or more, most preferably 1.14 g/cm³ or more, andpreferably 1.40 g/cm³ or less, more preferably 1.35 g/cm³ or less, stillmore preferably 1.30 g/cm³ or less, particularly preferably 1.25 g/cm³or less.

A tap density in this range provides sufficient filling properties, thusincreasing capacity. In addition, such a tap density tends to inhibitthe increase in intraparticle carbon density, thus providing goodrolling properties and making it easy to form a high-density negativeelectrode sheet.

Specific Surface Area (SA) Determined by BET Method

The specific surface area (SA) of the carbon material according to thisembodiment (e.g., but not limited to, Invention D), as determined by BETmethod, is preferably 2 m²/g or more, more preferably 2.5 m²/g or more,still more preferably 3 m²/g or more, particularly preferably 4 m²/g ormore, and preferably 30 m²/g or less, more preferably 20 m²/g or less,still more preferably 17 m²/g or less, particularly preferably 15 m²/gor less.

A specific surface area in this range tends to sufficiently secure siteswhere Li enters and exits, thus providing excellent input-outputcharacteristics, and tends to moderately control the activity of anactive material against electrolyte solution, thus inhibiting theincrease in initial irreversible capacity, as a result of which ahigh-capacity battery can be produced.

In this embodiment, the composite carbon material is produced by coatingirregularities of the surface of the carbon material to have reduceddibutyl phthalate (DBP) absorption and thus, when processed into acoating material in forming an electrode, can have a low viscosity,leading to improved coating properties.

“Coated” in this embodiment refers to a state in which at least part orall of the surface of the carbon material is coated or deposited with acarbonaceous material.

In this embodiment (e.g., but not limited to, Invention D), thecrystallite size (Lc) of the carbon material, as determined by X-raydiffractometry in accordance with the method of the Japan Society forPromotion of Scientific Research, is typically in the range of 30 nm ormore, preferably 50 nm or more, more preferably 100 nm or more, stillmore preferably 500 nm or more, particularly preferably 1,000 nm ormore. A crystallite size in this range provides particles having not toolow crystallinity, thus providing a non-aqueous secondary battery thereversible capacity of which is less likely to decrease. The lower limitof Lc is the theoretical value of graphite.

In one aspect of the composite carbon material according to oneembodiment of the present invention, the true density and the specificsurface area (SA) determined by BET method preferably satisfy aparticular relationship.

Specifically, the composite carbon material according to an embodimentof the present invention (e.g., but not limited to, Invention E)preferably satisfies the relationship of inequality (1E).

Inequality (1E)

Y _(e)−0.01X _(e)≦α  (1E)

(Y_(e)=true density (g/cm³), X_(e)=specific surface area (SA) (m²/g) ofcarbon material determined by BET method, α=2.20)

In the carbon material, a given by inequality (1E) is 2.20, preferably2.195, more preferably 2.19, still more preferably 2.16.

If the relationship represented by inequality (1E) is not satisfied, thebalance between usable regions in Li-ion insertion/extraction sites inthe particles and a carbonaceous material having such crystallinity thatfacilitates Li-ion insertion/extraction tends to be poor, thus resultingin degraded low-temperature output characteristics.

In this embodiment (e.g., but not limited to, Invention E), the truedensity of the composite carbon material is preferably 2.15 g/cm³ ormore, more preferably 2.16 g/cm³ or more, still more preferably 2.17g/cm³ or more, particularly preferably 2.18 g/cm³ or more, mostpreferably 2.19 g/cm³ or more, and preferably 2.26 g/cm³ or less, morepreferably 2.25 g/cm³ or less.

A true density in this range provides a moderate amount oflow-crystallinity structure, which facilitates Li-ioninsertion/extraction, thus providing good input-output characteristics.

Specific Surface Area (SA) Determined by BET Method

The specific surface area (SA) of the composite carbon materialaccording to this embodiment (e.g., but not limited to, Invention E), asdetermined by BET method, is preferably 2 m²/g or more, more preferably2.5 m²/g or more, still more preferably 3 m²/g or more, particularlypreferably 4 m²/g or more, and preferably 30 m²/g or less, morepreferably 20 m²/g or less, still more preferably 17 m²/g or less,particularly preferably 15 m²/g or less. A specific surface area in thisrange tends to sufficiently secure sites where Li enters and exits, thusproviding excellent input-output characteristics, and tends tomoderately control the activity of an active material againstelectrolyte solution, thus inhibiting the increase in initialirreversible capacity, as a result of which a high-capacity battery canbe produced.

90% Particle Diameter (d90) to 10% Particle Diameter (d10) Ratio(d90/d10) in Volume-Based Particle Size Distribution

The 90% particle diameter (d90) to 10% particle diameter (d10) ratio(d90/d10) in a volume-based particle size distribution of the compositecarbon material according to this embodiment (e.g., but not limited to,Invention E) is typically 2.0 or greater, preferably 2.2 or greater,more preferably 2.4 or greater, still more preferably 2.5 or greater,even more preferably 2.6 or greater, particularly preferably 2.7 orgreater, and typically 5.0 or less, preferably 4.5 or less, morepreferably 4.0 or less, still more preferably 3.8 or less, particularlypreferably 3.5 or less.

Average Value and Standard Deviation (σ_(R)) of Microscopic Raman RValues

In one aspect of one embodiment of the present invention, the compositecarbon material preferably comprises the carbon material (A) capable ofoccluding and releasing lithium ions and the carbonaceous material (B)on the surface of the carbon material (A), wherein the average value ofmicroscopic Raman R values of 30 randomly selected composite carbonmaterials is 0.1 to 0.85, and the standard deviation (σ_(R)) is 0.1 orless.

The average value of microscopic Raman R values of the composite carbonmaterial according to this embodiment (e.g., but not limited to,Invention F) is 0.1 to 0.85, preferably 0.15 or greater, more preferably0.2 or greater, still more preferably 0.23 or greater, particularlypreferably 0.25 or greater, and preferably 0.8 or less, more preferably0.65 or less, still more preferably 0.5 or less, particularly preferably0.4 or less.

The standard deviation is 0.1 or less, preferably 0.085 or less, morepreferably 0.08 or less, still more preferably 0.07 or less,particularly preferably 0.06 or less, and typically 0.001 or greater,preferably 0.01 or greater, more preferably 0.02 or greater.

The average value and the standard deviation (σ_(R)) of microscopicRaman R values described above are determined from 30 randomly selectedcomposite carbon materials according to an embodiment of the presentinvention using measurement methods described below.

An average value and a standard deviation (σ_(R)) of microscopic Raman Rvalues outside the above ranges mean that the surface of the carbonmaterial (A) is not uniformly coated with a carbonaceous material intoand from which Li ions are readily inserted and extracted. This tends tocause, for example, a concentrated excessive current flow into aspecific site where the carbonaceous material is sufficiently depositedand Li ions are readily inserted and extracted, particularly at lowtemperatures and during fast charging and discharging, so as to causeelectrodeposition, which impedes uniform and smooth insertion/extractionof Li ions, resulting in degraded low-temperature output characteristicsand cycle characteristics.

The Raman R values are determined by Raman microspectroscopy using aRaman spectroscope (e.g., Nicolet Almega XR available from Thermo FisherScientific) under the following conditions.

Target particles are gravity-dropped onto a sample stage, and Ramanmicrospectroscopy is performed with the surface of the target flat.

Excitation wavelength: 532 nm

Laser power on sample: 1 mW or less

Resolution: 10 cm⁻¹

Irradiation area: 1 μm

Measurement range: 400 cm⁻¹ to 4,000 cm⁻¹

Measurement of peak intensity: straight baseline subtraction in therange of about 1,100 cm⁻¹ to 1,750 cm⁻¹

Method for calculating Raman R value: In a spectrum after straightbaseline subtraction, a peak intensity I_(A) at the peak top of a peakP_(A) near 1,580 cm⁻¹ and a peak intensity I_(B) at the peak top of apeak P_(B) near 1,360 cm⁻¹ are read to calculate an R value(I_(B)/I_(A)). The average value and the standard deviation (σ_(R)) of30 randomly selected target particles are calculated.

Microscopic Raman R₁₅ Value

The microscopic Raman R₁₅ value given by equation (1F) of the compositecarbon material according to an embodiment of the present invention(e.g., but not limited to, Invention E) is typically 25% or less,preferably 15% or less, more preferably 12% or less, still morepreferably 9% or less, particularly preferably 5% or less, and typicallymore than 0%. A microscopic Raman R₁₅ value in this range indicates thatthe surface of the carbon material (A) is uniformly coated with thecarbonaceous material (B) and the surface of the carbon material (A) isless exposed. This enables uniform and smooth insertion/extraction of Liions, thus providing a composite carbon material with excellentlow-temperature output characteristics and cycle characteristics.

Microscopic Raman R ₍₁₅₎ value (%)=the number of composite carbonmaterials having a microscopic Raman R value of 0.15 or less among 30randomly selected composite carbon materials/30×100  (1F)

In one aspect of one embodiment of the present invention, the compositecarbon material preferably satisfies the relationship of inequality(1K). In inequality (1K), “carbon material” means “composite carbonmaterial”.

10.914>5x _(k) −y _(k)−0.0087a  Inequality (1K)

In inequality (1K), x_(k) is a true density [g/cm³] of the carbonmaterial; y_(k) is a value determined by equation (2K); and a is avolume-based average particle diameter [μm] of the carbon material.

y _(k)=(density [g/cm³] of carbon material under uniaxial load of 100kgf/3.14 cm²)−(tap density of carbon material [g/cm³])  Equation (2K)

In one aspect of the present invention, the carbon material according toanother embodiment of the present invention preferably satisfies therelationship of inequality (3K). In other words, the carbon materialaccording to an embodiment of the present invention (e.g., but notlimited to, Invention K) preferably satisfies inequality (1K) or (3K).

10.990 >5x _(k) −y _(k)  Inequality (3K)

(In inequality (3K), x_(k) is a true density [g/cm³] of the carbonmaterial, and y_(k) is a value determined by equation (2K).)

y _(k)=(density [g/cm³] of carbon material under uniaxial load of 100kgf/3.14 cm²)−(tap density of carbon material [g/cm³])  Equation (2K)

When the relationship represented by inequality (1K) or (3K) is notsatisfied, the particles tend to fracture in pressing an electrode inbattery production so as to cause flattening of the particles orseparation of the amorphous carbon, thus resulting in degradedlow-temperature output characteristics and a reduced capacity. Methodsfor measuring physical properties used to calculate inequality (1K) or(3K) will be described below.

Particle Density Under Uniaxial Load of 100 Kgf/3.14 cm²

The density under a uniaxial load of 100 kgf/3.14 cm² of the carbonmaterial according to this embodiment (e.g., but not limited to,Invention K) is preferably 0.7 g/cm³ or more, more preferably 0.9 g/cm³or more, still more preferably 1.2 g/cm³ or more, particularlypreferably 1.24 g/cm³ or more, and preferably 1.8 g/cm³ or less, morepreferably 1.7 g/cm³ or less, still more preferably 1.6 g/cm³ or less.

A density in this range can prevent particle fracture under a givenload, thus leading to excellent input-output characteristics.

The density under a uniaxial load of 100 kgf/3.14 cm² can be measuredusing an apparatus capable of measuring a load and a thickness under anygiven uniaxial pressure. For example, the measurement is made using anMCP-PD51 powder resistivity measurement system available from MitsubishiChemical Analytech Co., Ltd. First, values of the apparatus arecorrected. For a load correction, the load measured when the bottom of acylindrical container for accommodating the carbon material and a pushrod to be inserted into the container from above to apply pressure tothe carbon material are not in contact is confirmed to be 0 kgf/3.14cm². Next, a thickness gauge is corrected. While the cylindricalcontainer and the push rod are brought close using a hydraulic pump, azero-point correction is carried out such that the thickness gaugeindicates 0.00 mm when the load reaches 20 kgf/3.14 cm². After thecorrections are carried out, 3.0 g of the carbon material is placed inthe cylindrical container with a diameter of 2 cm, and the height of thecarbon material is adjusted so as to receive a load evenly. A seat islifted using the hydraulic pump, and the push rod is inserted into thecylindrical container. After the thickness gauge has indicated 15.0 mm,loads are measured at thicknesses at 0.5-mm intervals until the loadexceeds 1,000 kgf/3.14 cm². From the thicknesses obtained, the densitiesof the powder are calculated, and using Microsoft Excel, a graph iscreated with powder density plotted on the horizontal axis and load onthe vertical axis. A cubic spline curve of the graph is created, and theformula obtained is used to calculate a carbon material density under aload of 100 kgf/3.14 cm³. To reduce variation in measurements, themeasurement is made at least twice. When variation occurs, themeasurement is made three times, and the average of two closest valuesis used.

y _(k): (density [g/cm³] of carbon material under uniaxial load of 100kgf/3.14 cm²)−(tap density of carbon material [g/cm³])

The value of y in this embodiment (e.g., but not limited to, InventionK) is typically 0.10 or greater, more preferably 0.12 or greater, stillmore preferably 0.18 or greater, particularly preferably 0.19 orgreater, and preferably 1 or less, more preferably 0.9 or less, stillmore preferably 0.5 or less.

A value of y in this range causes less particle fracture under a givenload to reduce amorphous separation and particle deformation, thusproviding excellent input-output characteristics.

In one aspect of one embodiment of the present invention, the compositecarbon material has a large number of voids having fine structures inthe particles.

Specifically, the carbon material for a non-aqueous secondary batteryaccording to an embodiment of the present invention (e.g., but notlimited to, Inventions L¹ to L³) comprises a composite carbon materialmade of granulated particles satisfying (1L) and (2L) and further has acharacteristic particle cross section such that a box-counting dimensionis determined from an image of the particle cross section.

Carbon Material (Granulated Particles) Satisfying (1L) and (2L) inCarbon Material for Non-Aqueous Secondary Battery

The granulated particles in the carbon material for a non-aqueoussecondary battery satisfies the following:

(1) Being made of a carbonaceous material; and

(2) Satisfying the relationship |X₁−X|/X₁≦0.2, preferably ≦0.15, morepreferably ≦0.1, where X is a volume-based average particle diameterdetermined by laser diffraction, and X₁ is an equivalent circulardiameter determined from a cross-sectional SEM image.

If |X₁−X|/X₁ is too large, typical particles cannot be selected, whichresults in failure to express the overall tendency.

The volume-based average particle diameter X is defined as avolume-based median diameter determined by suspending 0.01 g of a carbonmaterial in 10 mL of a 0.2%, by mass aqueous solution of apolyoxyethylene sorbitan monolaurate surfactant (e.g., Tween 20(registered trademark)), placing the suspension (a measurement sample)in a commercially available laser diffraction/scattering particle sizedistribution analyzer (e.g., LA-920 available from HORIBA), irradiatingthe measurement sample with ultrasonic waves of 28 kHz at a power of 60W for 1 minute, and then performing a measurement with the analyzer.

The equivalent circular diameter X₁ determined from a cross-sectionalSEM image is expressed by the following formula using a particlecircumference L [μm].

$\begin{matrix}{X_{1} = \frac{L}{2\pi}} & \left\lbrack {{Mathematical}\mspace{14mu} 9} \right\rbrack\end{matrix}$

The granulated particles in the carbon material for a non-aqueoussecondary battery satisfies the relationship |R−R₁|≦0.1, preferably≦0.08, more preferably ≦0.06, where R is a roundness determined with aflow-type particle image analyzer, and R₁ is a roundness determined froma cross-sectional SEM image.

If |R−R₁| is too large, a particle boundary is not defined correctly butoverestimated, which may result in incorrect analysis.

As the value of the roundness R determined with a flow-type particleimage analyzer is used a value determined, for example, using aflow-type particle image analyzer (e.g., FPIA available from SysmexIndustrial Corp.) by dispersing about 0.2 g of a sample (the carbonmaterial for a non-aqueous secondary battery according to the presentinvention) in a 0.2% by mass aqueous solution (approximately 50 mL) of apolyoxyethylene (20) sorbitan monolaurate surfactant, irradiating thedispersion with ultrasonic waves of 28 kHz at a power of 60 W for 1minute, and then measuring the roundness of particles with a diameter inthe range of 1.5 to 40 μm with a detection range set to 0.6 to 400 μm.

The roundness R₁ determined from a cross-sectional SEM image iscalculated by the following formula using a particle area S [μm²]determined from a cross-sectional SEM image and a circumference L [μm].

$\begin{matrix}{R_{1} = \frac{4\pi \; S}{(L)^{2}}} & \left\lbrack {{Mathematical}\mspace{14mu} 10} \right\rbrack\end{matrix}$

The particle boundary may be defined by any method, and it may bedefined automatically or manually using commercially available analysissoftware. It is preferable to approximate a particle by a polygon, andin this case, an approximation by a polygon with 15 or more sides ismore preferred. This is because if a polygon with less than 15 sides isused, a background portion may be determined to be a part of theparticle in approximating a curve.

Acquisition of Particle Cross-Sectional Image

For the image of a particle cross section is used a reflected electronimage acquired at an acceleration voltage of 10 kV using a scanningelectron microscope (SEM). An SEM observation sample for acquiring aparticle cross-sectional image may be prepared by any method, and aparticle cross-sectional image is acquired using an SEM after a sampleis prepared by cutting an electrode plate containing the carbon materialfor a non-aqueous secondary battery, a film coated with the carbonmaterial for a non-aqueous secondary battery, with a focused ion beam(FIB) or ion milling to obtain a particle cross section.

The acceleration voltage in observing the cross section of the carbonmaterial for a non-aqueous secondary battery with a scanning electronmicroscope (SEM) is 10 kV.

This acceleration voltage makes a difference between a reflectedelectron SEM image and a secondary electron SEM image to allow voidregions and other regions of the carbon material for a non-aqueoussecondary battery to be easily distinguished. The imaging magnificationis typically 500× or more, more preferably 1,000× or more, still morepreferably 2,000× or more, and typically 10,000 or less. An imagingmagnification in this range enables the acquisition of an entire imageof one particle of the carbon material for a non-aqueous secondarybattery. The resolution is 200 dpi (ppi) or more, preferably 256 dpi(ppi) or more. The number of picture elements suitable for evaluation isat least 800 pixels.

Average Box-Counting Dimension Relative to Void Regions inCross-Sectional SEM Image

The carbon material for a non-aqueous secondary battery has an averagebox-counting dimension relative to void regions of 1.55 or greater,preferably 1.60 or greater, more preferably 1.62 or greater, andtypically 1.80 or less, preferably 1.75 or less, more preferably 1.70 orless, as calculated from images obtained by randomly selecting 30granulated particles satisfying (1L) and (2L) above from across-sectional SEM image, dividing the cross-sectional SEM image ofeach granulated particle into void regions and non-void regions, andbinarizing the image.

An excessively small average box-counting dimension relative to voidregions means that the amount of finer structure is small, in which caseexcellent output characteristics, one of the effects of the presentinvention, cannot be provided. An excessively large average box-countingdimension increases the specific surface area of the particles, leadingto low initial efficiency.

The box-counting dimensions of the particles of the carbon material fora non-aqueous secondary battery are determined taking the following (a)to (d) into account.

(a) Definition and Calculation Method of Box-Counting Dimension

Box-counting dimension is a method for estimating a fractal dimension byobserving a certain area split into certain sizes (box sizes) to examinehow much fractal patterns are contained (see JP 2013-77702 A).Box-counting dimension is an indicator of shape complexity, the degreeof surface irregularity, and others, and larger fractal dimensionsindicate more complex irregularities. The fractal dimension is definedby the following formula, where Nδ (F) is the number of square boxes ofside δ necessary for covering a pattern F.

$\begin{matrix}{D = {\lim\limits_{\delta\rightarrow 0}\frac{N_{\delta}(F)}{\log \; \delta}}} & \left\lbrack {{Mathematical}\mspace{14mu} 11} \right\rbrack\end{matrix}$

In this embodiment (e.g., but not limited to, Invention L¹), across-sectional SEM image of a particle composed of voids and carbon issplit into grid areas (boxes) at regular intervals δ (split into squaresubareas of side δ), and the number of boxes containing voids is countedwith varying values of δ. Next, a double logarithmic graph is createdwith the number of boxes counted plotted on the vertical axis and δ onthe horizontal axis, and a fractal dimension is determined from theslope of the graph.

Specifically, in a cross-sectional SEM image of a particle composed ofvoids and carbon, voids and other regions of the particle are binarized.The binarization is performed in units of pixels of the image. Analysisobjects are portions representing pixels of voids among the binarizedregions. The region outside the particle (outside the outline of theparticle) requires value conversion so as not to be regarded as a void.The image is split into grid areas (boxes) having a specific pixel size.Although the boxes may be arranged in any manner, they are preferablyarranged parallel to the major axis (the longest diameter passingthrough the barycenter) of the particle. In the arrangement, the imageis split into boxes as shown in FIGS. 7 and 8. The number of split boxesincluding at least one pixel representing a void is counted. The sameprocedure is repeated with varying box sizes, and a double logarithmicgraph is created with the number of boxes counted plotted on thevertical axis and the box size δ on the horizontal axis. A linearapproximation of this plot is performed, and the slope of the line ismultiplied by −1. The product obtained is the fractal dimensionaccording to the box-counting method. The slope may be calculated by theleast-squares method.

The fractal dimension is an indicator of the degree of self-similarity,and in expressing a binarized image, it serves as an indicator of thecomplexity and the fineness of a structure. This means that in abinarized image having a more complicated partial structure, theproportion of fine structure in a box tends to increase, that is, theslope tends to be steeper with decreasing box size, and the fineness ofthe partial structure and the amount of such structure are expressed. Inother words, the box-counting dimension in the present invention is anindicator of the complexity of a fine structure of voids and the amountof such structure.

(b) Definition of Box Size

The image may be split into any box size, but based on the maximum pixelof the image, it is preferably split into 10 parts or more, morepreferably 15 parts or more, particularly preferably 20 parts or more,and typically 50 parts or less, preferably 40 parts or less, morepreferably 30 parts or less, on a logarithmic graph. A box size in thisrange reduces the possibility that differences between picture elementsoccur and eliminates the need for a high-resolution image.

(c) Method of Binarization

The binarization may be carried out by any method by whichintra-particle voids and carbon portions are clearly distinguished fromeach other, as shown in FIG. 9. The binarization, when performed on an8-bit gray-scale image, such as an SEM image, refers to dividingluminances into two and representing the two divided images in twovalues (e.g., 0 and 255, in the case of 8-bit). The binarization may becarried out using any desired image processing software. The division bysetting a threshold can be carried out using any algorithm, such as themode method and the ISOData method, by which void portions and carbonportions can be clearly distinguished from each other. The target imageneeds to be a binarizable image. The binarizable image, in this case,refers to an image in which the luminance of void portions and theluminance of carbon portions are clearly distinguished from each otherby a certain threshold. In some images, the surface may be rough due tolow processing accuracy; the cross section may be facing obliquely; orthe luminances of void portions and carbon portions may be close to eachother depending on the settings such as contrast and brightness. Suchimages may show incorrect void distributions when binarized and thus arepreferably excluded from analysis objects. For example, FIG. 10 is animage in which the surface of a graphite portion in the middle has arough pattern and a low luminance, and fine voids have high luminances.When such an image is binarized picking up fine parts, carbon portionsare also expressed as voids; by contrast, if a luminance at a carbonportion with no void is used as a threshold, fine voids, which areactually voids, cannot be displayed. Although such particles arepreferably not selected, the cross section of such particles may betypical, and thus it is necessary not to analyze such an SEM imageunsuitable for binarization but to retake an image and adjust thebrightness and the contrast.

(d) Definition of Particle Boundary

The particle boundary may be established by any method, for example, byfreehand or the approximation by a polygon, provided that the boundaryneeds to be clearly defined. Although there is no limitation, it isnecessary to establish the boundary between the particle and otherregions such that the region of interest (ROI) representing the shape ofthe particle is completely included. When the boundary is not a simpleoval but has a complicated shape, for example, the boundary may bedivided into any desired number of equally spaced sections toapproximate the particle region by a polygon. The boundary, however, isestablished so as not to deviate from a roundness R determined with aflow-type particle image analyzer. As used herein, “not deviate” meansthat a degree of spheroidization R determined by a flow-type particleimage analyzer and a degree of spheroidization R₁ determined from across-sectional SEM image satisfy the relationship |R−R₁|≦0.1. When anelectrode coated with a binder having poor conductivity is used, theboundary may be difficult to determine under the measurement conditionsof the present invention. This is a phenomenon that occurs due to thepoor conductivity of the binder when the side of the particle is visiblein depth of the cross section of the particle. In such a case, it isnecessary to take another image with a clear boundary at a loweracceleration voltage to determine a boundary.

In one aspect of one embodiment of the present invention, the carbonmaterial for a non-aqueous secondary battery comprises uniformlydispersed intra-particle pores.

Specifically, the carbon material for a non-aqueous secondary batteryaccording to an embodiment of the present invention (e.g., but notlimited to, Invention L²) comprises a composite carbon material made ofgranulated particles satisfying (1L) and (2L) above and further has acharacteristic particle cross section such that the void dispersity D ofthe present invention is determined from an image of the particle crosssection.

Void Dispersity D in Cross-Sectional SEM Image

The carbon material for a non-aqueous secondary battery typically has anaverage dispersity D of 30 particles, as determined by the followingmeasurement method using 30 granulated particles satisfying (1L) and(2L) above randomly selected from a cross-sectional SEM image, of 60% ormore, preferably 61% or more, more preferably 62% or more, and typically90% or less, preferably 85% or less, more preferably 80% or less.

Measurement Method

Using a cross-sectional SEM image, grid lines are drawn to split theminor axis and the major axis of a target granulated particle each into20 parts. Using cells in the grid, the granulated particle iscompartmentalized as defined below. The expectation E of void area ofeach compartment is calculated using equation (A) below, and thedispersity D of the granulated particle is calculated using equation (B)below.

The cross-sectional SEM image is a reflected electron image acquired atan acceleration voltage of 10 kV.

How to Create Grid

Using a cross-sectional SEM image, grid lines are drawn to split theminor axis and the major axis of a target granulated particle each into20 parts, as shown in FIG. 11. This image needs to be parallel to theparticle major axis and the image.

Definition of Compartment

The compartment is defined as a granulated particle portion and/or aregion where a void is present in the granulated particle in each cellof the grid. The outside of the boundary of the granulated particle isexcluded from the compartment. For grid cells that are divided by theparticle boundary into two, as shown in FIG. 12, the region includingthe particle is defined as a compartment.

Definition of Expectation

For compartments defined by grid lines and the particle boundary, theexpectation E of a void area corresponding to each compartment area isdetermined from equation (A).

Expectation E [μm²] of void area in target compartment=(gross area [μm²]of internal voids of one target granulated particle)/(cross-sectionalarea [μm²] of one target granulated particle)×(area [μm²] of targetcompartment)  Equation (A)

The expectation E of a compartment defined by the particle boundary iscalculated to be smaller than the expectation E of a grid cell accordingto the area of the compartment.

Definition of Dispersity D

The dispersity D, an indicator of the void dispersity in a particle, iscalculated by equation (B).

Dispersity D (%)=(sum total [μm²] of areas of compartments that satisfy(gross area [μm²] of voids in target compartment)/(expectation E [μm²]of void area in target compartment)=0.5 or greater)/(sum total [μm²] ofareas of all the compartments of one target granulatedparticle)×100  Equation (B)

The dispersity D indicates how voids are dispersed throughout the insideof a particle, excluding compartments having only a small void area.

The equation (A) and the equation (B) of the carbon material for anon-aqueous secondary battery are calculated taking the following (a) to(d) into account.

(a) Method of Selecting Granulated Particles and Definition of MajorAxis and Minor Axis

The particle boundary may be established by any method by which theboundary is clearly defined, provided that the boundary between theparticle and other regions needs to be established such that the regionof interest (ROI) representing the shape of the particle is completelyincluded. For example, it may be established by freehand or theapproximation by a polygon. When the boundary is not a simple oval buthas a complicated shape, for example, the boundary may be divided intoany desired number of equally spaced sections to approximate theparticle region by a polygon. The boundary, however, is established soas not to deviate from a roundness R determined with a flow-typeparticle image analyzer. As used herein, “not deviate” means that adegree of spheroidization R determined by a flow-type particle imageanalyzer and a degree of spheroidization R₁ determined from across-sectional SEM image satisfy the relationship |R−R₁|≦0.1. When anelectrode coated with a binder having poor conductivity is used, theboundary may be difficult to determine under the measurement conditionsof the present invention. This is a phenomenon that occurs due to thepoor conductivity of the binder when the side of the particle is visiblein the cross section of the particle. In such a case, it is necessary totake another image with a clear boundary at a lower acceleration voltageto determine a boundary.

For one randomly selected granulated particle, the barycenter (centroid)is defined. First, the particle defined by the boundary is approximatedby square cells. The size of each cell is preferably, but notnecessarily, 5 nm or less in actual size. Two-dimensional coordinatesare determined in the image. The coordinates of the barycenter of eachcell are defined. Assuming that the weights of the cells are the same,the cells are numbered from 1 to N. The following formula is used todetermine the coordinates of the barycenter of the granulated particle.

$\begin{matrix}{\overset{\rightarrow}{r_{G}} = \frac{\sum_{1}^{N}\overset{\rightarrow}{r_{i}}}{N}} & \left\lbrack {{Mathematical}\mspace{14mu} 12} \right\rbrack\end{matrix}$

In the formula, r_(i) represents the coordinates of an i-th cell, andr_(G) represents the coordinates of the barycenter. The barycenter maybe determined by operating any desired image software, or by thefollowing formula if the barycenter of each divided mesh can be definedby any given figure.

$\begin{matrix}{\overset{\rightarrow}{r_{G}} = \frac{\sum_{1}^{N}{A_{i}\overset{\rightarrow}{r_{i}}}}{\sum_{1}^{N}A_{i}}} & \left\lbrack {{Mathematical}\mspace{14mu} 13} \right\rbrack\end{matrix}$

In the formula, A_(i) is the area of an i-th figure, and r_(i) is thebarycentric (centroid) coordinates of the i-th figure.

Next, the longest line segment among line segments passing through thebarycenter obtained and bounded by the boundary fixed as described aboveis defined as a major axis. The line segment orthogonal to the majoraxis among line segments passing through the barycenter and bounded bythe boundary fixed as described above is defined as a minor axis.

(b) Definition of Void Region and Non-Void Region and Method ofCalculating their Areas

The binarization may be carried out by any method by whichintra-particle voids and carbon portions are clearly distinguished fromeach other, as shown in FIG. 9, and is preferably carried out such thatvoid regions and other carbon particle regions are clearly distinguishedfrom each other. The binarization, when performed on an 8-bit gray-scaleimage, such as an SEM image, refers to dividing luminances into two andrepresenting the two divided images in two values (e.g., 0 and 255, inthe case of 8-bit). The binarization is not particularly limited to, andmay be carried out using any desired image processing software. Thedivision by setting a threshold can be carried out using any algorithm,such as the mode method and the ISOData method, by which void portionsand carbon portions can be clearly distinguished from each other. Theimage needs to be a binarizable image. The binarizable image, in thiscase, refers to an image in which the luminance of void portions and theluminance of carbon portions are clearly distinguished from each otherby a certain threshold. In some images, the surface may be rough due tolow processing accuracy; the cross section may be facing obliquely; orthe luminances of void portions and carbon portions may be close to eachother depending on the settings such as contrast and brightness. Suchimages may show incorrect void distributions when binarized and thus arepreferably excluded from analysis objects. For example, FIG. 10 is animage in which the surface of a graphite portion in the middle has arough pattern and a low luminance, and fine voids have high luminances.When such an image is binarized picking up fine parts, carbon portionsare also expressed as voids; by contrast, if a luminance at a carbonportion with no void is used as a threshold, fine voids, which areactually voids, cannot be displayed. Although such particles arepreferably not selected, the cross section of such particles may betypical, and thus it is necessary not to analyze such an SEM imageunsuitable for binarization but to retake an image and adjust thebrightness and the contrast.

The areas of the void region and the non-void region in the particlethus calculated are each calculated as an approximation in a pixel unitand converted into an actual unit.

(c) Creation of Grid

In the binarized image is created cells that split the minor axis andthe major axis of the granulated particle each into 20 parts. The cellsmay be arranged such that they are parallel to the major axis and theminor axis of the granulated particle.

(d) Calculation of Expectation E and Dispersity D of Target Compartment

For each of the 400 cells created by splitting the minor axis and themajor axis of the granulated particle each into 20 parts, theexpectation E is calculated by equation (A) above. The sum total ofareas of compartments having an expectation E of 0.5 or greater iscalculated, and the dispersity D is calculated by equation (B) above.

For each of the 30 granulated particles selected, the dispersity D iscalculated, and the average dispersity D of the 30 particles iscalculated.

In one aspect of the present invention, the carbon material for anon-aqueous secondary battery comprises intra-particle voids theorientation of which and the interval between which are controlled.

Specifically, the carbon material for a non-aqueous secondary batteryaccording to an embodiment of the present invention (e.g., but notlimited to, Invention L³) comprises a composite carbon material made ofgranulated particles satisfying the following (1L) and (2L) and furtherhas a characteristic particle cross section such that the ratio (Zave/X)of average inter-void distance Z (Zave) of 30 particles to volume-basedaverage particle diameter X determined by laser diffraction of thepresent invention is determined from an image of the particle crosssection.

Zave/X

The carbon material for a non-aqueous secondary battery according tothis embodiment (e.g., but not limited to, Invention L³) comprisesgranulated particles satisfying (1L) and (2L) above and has an averageinter-void distance Z (Zave) of 30 particles as defined below and avolume-based average particle diameter X determined by laser diffractionin a ratio (Zave/X) of typically 0.060 or less, preferably 0.055 orless, more preferably 0.050 or less, still more preferably 0.045 orless, and typically 0.001 or greater, preferably 0.010 or greater, morepreferably 0.020 or greater, the 30 granulated particles satisfying (1L)and (2L) and being randomly selected from a cross-sectional SEM image.

An excessively large Zave/X means that the distance between the carbonmaterial and voids constituting the granulated particle is wide, whichdisadvantageously results in a low liquid retention in the particle.

Definition of Average Inter-Void Distance Z (Zave) of 30 Particles

As shown in the left figure of FIG. 13, three lines are drawn that areparallel to the minor axis of a target granulated particle and split themajor axis of the granulated particle into four parts, and inter-voiddistances Z (μm) of the granulated particle on each line (see the rightfigure of FIG. 13) are each measured. The average of 30 particles intotal is calculated. This is defined as the average inter-void distanceZ (Zave) of 30 particles.

W/X

In this embodiment (e.g., but not limited to, Invention L³), the carbonmaterial for a non-aqueous secondary battery comprises granulatedparticles satisfying (1L) and (2L) above and has a standard deviation(W) of void sizes Y of 30 particles as defined below and a volume-basedaverage particle diameter X determined by laser diffraction in a ratio(W/X) of preferably 0.018 or less, more preferably 0.016 or less, stillmore preferably 0.014 or less, and typically 0.001 or greater,preferably 0.005 or greater, more preferably 0.008 or greater, the 30granulated particles satisfying (1L) and (2L) above and being randomlyselected from a cross-sectional SEM image.

W/X is a quotient of a standard deviation of void sizes divided by aparticle size, and a larger value of W/X means that a higher proportionof relatively large voids.

A W/X in the above range means relatively uniform void sizes or a lowproportion of large voids, i.e., a fine void structure that allows anelectrolyte solution to uniformly permeate into the particles.

Definition of Standard Deviation (W) of Void Sizes Y (μm) of 30Particles

As shown in the left figure of FIG. 13, three lines are drawn that areparallel to the minor axis of a target granulated particle and split themajor axis of the granulated particle into four parts, and void sizes Y(μm) of the granulated particle on each line (see the right figure ofFIG. 13) are each measured. The standard deviation of 30 particles intotal is calculated. This is defined as the standard deviation (W) ofvoid sizes Y of 30 particles.

The standard deviation is determined by the following formula, whereYave is the average of Y, and Ny is the number of Y.

$\begin{matrix}{W = \left( \frac{\sum\left( {Y - Y_{ave}} \right)^{2}}{Ny} \right)^{1/2}} & \left\lbrack {{Mathematical}\mspace{14mu} 14} \right\rbrack\end{matrix}$

Condition of Voids

Preferably, the granulated particles in the carbon material for anon-aqueous secondary battery according to the present invention haveslit-like voids, and the slit-like voids are arranged mainly in layers.

More specifically, among 30 granulated particles satisfying (1L) and(2L) above randomly selected from a cross-sectional SEM image, theproportion (by number) of particles having slit-like voids arrangedmainly in layers is more preferably 70% or more, particularly preferably80% or more, most preferably 90% or more. Within this range, it can besaid that most of the particles have a slit-like and layered structure.

“Slit-like void” refers to a long and narrow void (with a high aspectratio) like a gap. The aspect ratio of the void is preferably 10 orgreater, more preferably 15 or greater. The aspect ratio is a valueobtained by dividing the major axis of the void by the minor axis, thatis, (major axis of void)/(minor axis of void). The major axis and theminor axis of the void can be calculated by the same method as inSelection of Granulated Particles and Definition of Minor Axis describedbelow.

In the present invention, “voids in layers” means that major axes ofvoids in a particle are arranged in parallel. For example, if the anglebetween the major axes of two voids is within ±30°, the two voids areregarded as being in parallel.

The proportion of the area of voids in layers (the area of voids inlayers/the gross area of voids) in a granulated particle is preferably40% or more, more preferably 50% or more, still more preferably 60% ormore, and typically 100% or less, preferably 90% or less. The proportionof the number of slit-like voids (the number of slit-like voids/thetotal number of voids) is preferably 70% or more, more preferably 80% ormore, still more preferably 90% or more, and typically 100% or less,preferably 90% or less. If the number and the area of slit-like voidsare in these ranges, it can be said that the particle has so many fineslit-like structures that provide more reaction initiation surfaces ofLi and sufficient permeability of electrolyte solution.

The above-described Zave/X and W/X of the carbon material for anon-aqueous secondary battery are calculated taking the following (a) to(d) into account.

(a) Selection of Granulated Particles and Definition of Minor Axis

In an SEM image acquired, 30 granulated particles satisfying the aboveconditions (1L) and (2L) are randomly selected. In the selection,particle boundaries are established along the outlines of the granulatedparticles. The particle boundary may be established by any method bywhich the boundary is clearly defined. For example, it may beestablished by freehand or the approximation by a polygon. It isnecessary to establish the boundary between the particle and otherregions such that the region of interest (ROI) representing the shape ofthe particle is completely included. When the boundary is notlinear-like but has a complicated shape, for example, the boundary maybe divided into any desired number of equally spaced sections toapproximate the particle region by a polygon. The boundary isestablished so as not to deviate from a roundness R determined with aflow-type particle image analyzer. As used herein, “not deviate” meansthat a degree of spheroidization R determined by a flow-type particleimage analyzer and a degree of spheroidization R₁ determined from across-sectional SEM image satisfy the relationship |R−R₁|≦0.1.

For one randomly selected granulated particle, the barycenter (centroid)is defined. First, the particle defined by the boundary is approximatedby square cells. The size of each cell is preferably, but notnecessarily, 5 nm or less in actual size. Two-dimensional coordinatesare determined in the image. The coordinates of the barycenter of eachcell are defined. Assuming that the weights of the cells are the same,the cells are numbered from 1 to N. The following formula is used todetermine the coordinates of the barycenter of the granulated particle.

$\begin{matrix}{\overset{\rightarrow}{r_{G}} = \frac{\sum_{1}^{N}\overset{\rightarrow}{r_{i}}}{N}} & \left\lbrack {{Mathematical}\mspace{14mu} 15} \right\rbrack\end{matrix}$

In the formula, r_(i) represents the coordinates of an i-th cell, andr_(G) represents the coordinates of the barycenter. The barycenter maybe determined by operating any desired image software, or by thefollowing formula if the barycenter of each divided mesh can be definedby any given figure.

$\begin{matrix}{\overset{\rightarrow}{r_{G}} = \frac{\sum_{1}^{N}{A_{i}\overset{\rightarrow}{r_{i}}}}{\sum_{1}^{N}A_{i}}} & \left\lbrack {{Mathematical}\mspace{14mu} 16} \right\rbrack\end{matrix}$

In the formula, A_(i) is the area of an i-th figure, and r_(i) is thebarycentric (centroid) coordinates of the i-th figure.

Next, the longest line segment among line segments passing through thebarycenter obtained and bounded by the boundary fixed as described aboveis defined as a major axis. The line segment orthogonal to the majoraxis among line segments passing through the barycenter and bounded bythe boundary fixed as described above is defined as a minor axis.

(b) Definition and Calculation Method of Intra-Particle Voids

The binarization may be carried out by any method by whichintra-particle voids and carbon portions are clearly distinguished fromeach other, as shown in FIG. 9. It is supposed that the image to beprocessed is an 8-bit gray-scale image, the luminance of one pictureelement (1 Pixel) of which is expressed by a natural number from 0 to255. The binarization refers dividing luminances into two andrepresenting the two divided images in two values (e.g., 0 and 255 inthis case). The binarization may be carried out using any desired imageprocessing software. The division by setting a threshold can be carriedout using any algorithm, such as the mode method and the ISOData method,by which void portions and carbon portions can be clearly distinguishedfrom each other. The target image needs to be a binarizable image. Thebinarizable image, in this case, refers to an image in which theluminance of void portions and the luminance of carbon portions areclearly distinguished from each other by a certain threshold. In someimages, the surface may be rough due to low processing accuracy; thecross section may be facing obliquely; or the luminances of voidportions and carbon portions may be close to each other depending on thesettings such as contrast and brightness. Such images may show incorrectvoid distributions when binarized and thus are preferably excluded fromanalysis objects. For example, FIG. 10 is an image in which the surfaceof a graphite portion in the middle has a rough pattern and a lowluminance, and fine voids have high luminances. When such an image isbinarized picking up fine parts, carbon portions are also expressed asvoids; by contrast, if a luminance at a carbon portion with no void isused as a threshold, fine voids, which are actually voids, cannot bedisplayed. Although such particles are preferably not selected, thecross section of such particles may be typical, and thus it is necessarynot to analyze such an SEM image unsuitable for binarization but toretake an image and adjust the brightness and the contrast.

(c) Voids on Line Segment of Granulated Particle

“Voids in a granulated particle intersecting the minor axis of thegranulated particle” refers to voids on three line segments that areparallel to the minor axis of the granulated particle and split themajor axis of the granulated particle into four parts (see FIG. 13).Picture elements intersecting line segments translated from the threeline segments parallel to the minor axis of the granulated particle inthe major axis direction by ±0.5 pixel are regarded as voids on theminor axis.

(d) Average Interval (Zave) Between Voids and Standard Deviation (W) ofVoid Sizes

The interval between voids (the distance between a void and a void) inone randomly selected granulated particle is determined on theabove-described three line segments parallel to the minor axis of thegranulated particle (see FIG. 13). In one granulated particle, distancesZ between voids on the three line segments parallel to the minor axisare each measured. This measurement is made on 30 particles. Its averagevalue is defined as the average inter-void distance Z (Zave) of 30particles.

Furthermore, sizes Y of voids on the three line segments (see FIG. 13)are each measured. This measurement is made on 30 particles. Itsstandard deviation is defined as the standard deviation (W) of voidsizes Y of 30 particles.

In this embodiment (e.g., but not limited to, Invention L³), voids inthe granulated particle are preferably arranged, mainly, relativelyparallel to the major axis of the granulated particle.

Negative Electrode for Non-Aqueous Secondary Battery

The present invention also relates to a negative electrode comprisingthe carbon material of the present invention described above. There isno limitation on the basic configuration and the production method ofthe negative electrode of the present invention. Hereinafter, the carbonmaterial includes a composite carbon material and a mixed carbonmaterial unless otherwise specified. The negative electrode (hereinafteralso referred to as “electrode sheet” as appropriate) for a non-aqueoussecondary battery comprising the carbon material of the presentinvention or a carbon material produced by the method of the presentinvention comprises a current collector and a negative electrode activematerial layer on the current collector, the active material layercomprising the carbon material of the present invention or a carbonmaterial produced by the method of the present invention. Morepreferably, the active material layer comprises a binder.

Any binders may be used, but those having olefinic unsaturated bonds intheir molecules are preferred. Specific examples include, but are notlimited to, styrene-butadiene rubbers, styrene-isoprene-styrene rubbers,acrylonitrile-butadiene rubbers, butadiene rubbers, andethylene-propylene-diene copolymers. These binders, having olefinicunsaturated bonds, can inhibit the active material layer from beingswollen by an electrolyte solution. In particular, styrene-butadienerubbers are preferred from the viewpoint of availability.

Combining the carbon material, an active material, of the presentinvention with such a binder having an olefinic unsaturated bond canincrease the strength of a negative electrode plate. A negativeelectrode with increased strength is less prone to degradation bycharging and discharging, leading to a prolonged cycle life.Furthermore, in the negative electrode according to the presentinvention, the adhesive strength between the active material layer andthe current collector is high. Thus, even if the amount of binder in theactive material layer is small, the active material layer will notprobably be peeled off the current collector when the negative electrodeis wound to produce a battery.

Preferred binders having olefinic unsaturated bonds in their moleculesare those having high molecular weights and/or those having highproportions of unsaturated bonds. Specifically, in the case of bindershaving high molecular weights, preferred are those having weight averagemolecular weights preferably in the range of 10,000 or greater, morepreferably 50,000 or greater, and preferably 1,000,000 or less, morepreferably 300,000 or less. In the case of binders having highproportions of unsaturated bonds, preferred are those having olefinicunsaturated bonds in a molar amount preferably in the range of 2.5×10⁻⁷mol or more, more preferably 8×10⁻⁷ mol or more, and preferably 1×10⁻⁶mol or less, more preferably 5×10⁻⁶ mol or less, per gram of thebinders. Although the binder is only required to satisfy one of theregulation of molecular weight and the regulation of proportion ofunsaturated bonds, those satisfying both the regulations are morepreferred. A molecular weight of a binder having an olefinic unsaturatedbond in this range provides high mechanical strength and flexibility.

The binder having an olefinic unsaturated bond preferably has a degreeof unsaturation of 15% or more, more preferably 20% or more, still morepreferably 40% or more, and preferably 90% or less, more preferably 80%or less. The degree of unsaturation is a proportion (%) of double bondsrelative to repeating units of a polymer.

In the present invention, a binder having no olefinic unsaturated bondcan be used in combination with the above-described binder having anolefinic unsaturated bond to the extent that the effects of the presentinvention are eliminated. The binder having no olefinic unsaturated bondis added in an amount preferably in the range of 150% by mass or less,more preferably 120% by mass or less, relative to the binder having anolefinic unsaturated bond.

Combined use of a binder having no olefinic unsaturated bond can improvecoating properties, but an excessive amount of binder reduces thestrength of the active material layer.

Examples of binders having no olefinic unsaturated bond includepolysaccharide thickeners, such as methylcellulose,carboxymethylcellulose, starch, carrageenan, pullulan, guar gum, andxanthan gum (xanthane gum); polyethers, such as polyethylene oxide andpolypropylene oxide; vinyl alcohols, such as polyvinyl alcohol andpolyvinyl butyral; polyacids, such as polyacrylic acid andpolymethacrylic acid; metal salts of these polymers; fluorine-containingpolymers, such as polyvinylidene fluoride; alkane polymers, such aspolyethylene and polypropylene; and copolymers thereof.

When the carbon material according to the present invention is used incombination with the above-described binder having an olefinicunsaturated bond, the ratio of the binder in the active material layercan be smaller than before. Specifically, the mass ratio of the carbonmaterial according to the present invention to a binder (which mayoptionally be a mixture of a binder having an unsaturated bond and abinder having no unsaturated bond as described above) is preferably inthe range of 90/10 or greater, more preferably 95/5 or greater, andpreferably 99.9/0.1 or less, more preferably 99.5/0.5 or less, on a drymass basis. A binder in a ratio in this range can prevent or reduce thedecrease in capacity and the increase in resistance, and furtherprovides an electrode plate with high strength.

The negative electrode is formed by dispersing the carbon material andthe binder described above in a dispersion medium to prepare a slurryand applying the slurry to a current collector. Examples of dispersionmedia that can be used include organic solvents, such as alcohols, andwater. To the slurry, a conductive agent (conductive auxiliary) mayoptionally be added. Examples of conductive agents include carbonblacks, such as acetylene black, Ketjen black, and furnace black, andfine powders of Cu, Ni, and alloys thereof with an average particlediameter of 1 μm or less. The amount of conductive agent is preferablyabout 10% by mass or less relative to the carbon material of the presentinvention.

The current collector to which the slurry is applied may be those knownin the art. Specific examples include thin metal films such as rolledcopper foil, electrolytic copper foil, and stainless foil. The thicknessof the current collector is preferably 4 μm or more, more preferably 6μm or more, and preferably 30 μm or less, more preferably 20 μm or less.

The slurry, after being applied to the current collector, is dried indry air or an inert atmosphere at a temperature of preferably 60° C. orhigher, more preferably 80° C. or higher, and preferably 200° C. orlower, more preferably 195° C. or lower, to form an active materiallayer.

The active material layer obtained by applying and drying the slurrypreferably has a thickness of 5 μm or more, more preferably 20 μm ormore, still more preferably 30 μm or more, and preferably 200 μm orless, more preferably 100 μm or less, still more preferably 75 μm orless. The thickness of the active material layer in this range iswell-balanced with the particle diameter of the active material toprovide a highly practical negative electrode that sufficiently occludesand releases Li at a high-density current.

The thickness of the active material layer may be adjusted to be athickness in the above range by pressing the slurry that has beenapplied and dried.

In applications where capacity is important, the density of the carbonmaterial in the active material layer is preferably 1.55 g/cm³ or more,more preferably 1.6 g/cm³ or more, still more preferably 1.65 g/cm³ ormore, particularly preferably 1.7 g/cm³ or more, and preferably 1.9g/cm³ or less, although the density varies depending on the application.A density in this range can ensure a sufficient battery capacity perunit volume and reduces the possibility of degradation of ratecharacteristics.

For example, in applications where input-output characteristics areimportant, such as automotive applications and power tool applications,the density is typically 1.1 g/cm³ to 1.65 g/cm³. A density in thisrange can avoid increases in contact resistance between particles, whichmight occur at an excessively low density, and, on the other hand, canprevent or reduce the degradation of rate characteristics, which mightoccur at an excessively high density. In these applications, the densityis preferably 1.2 g/cm³ or more, more preferably 1.25 g/cm³ or more.

In applications where capacity is important, including mobile deviceapplications such as cellular phones and personal computers, the densitycan be typically 1.45 g/cm³ or more, and typically 1.9 g/cm³ or less. Adensity in this range can avoid decreases in battery capacity per unitvolume, which might occur at an excessively low density, and, on theother hand, can prevent or reduce the degradation of ratecharacteristics, which might occur at an excessively high density. Inthese applications, the density is preferably 1.55 g/cm³ or more, morepreferably 1.65 g/cm³ or more, particularly preferably 1.7 g/cm³ ormore.

When a negative electrode for a non-aqueous secondary battery isproduced using the carbon material described above, there is nolimitation on the method and the selection of other materials.Furthermore, when a lithium ion secondary battery is produced using thisnegative electrode, there is no limitation on the selection of membersthat constitute the lithium ion secondary battery and are essential fora battery configuration, such as a positive electrode and an electrolytesolution. Hereinafter, a detailed description will be given of anegative electrode for a lithium ion secondary battery comprising thecarbon material of the present invention and a lithium ion secondarybattery comprising the carbon material of the present invention, but thefollowing specific examples of usable materials, production methods, andothers should not be construed as limiting.

Non-Aqueous Secondary Battery

The non-aqueous secondary battery, particularly, the lithium ionsecondary battery, the basic configuration of which is the same as thoseof lithium ion secondary batteries known in the art, typically comprisesa positive electrode and a negative electrode, each being capable ofoccluding and releasing lithium ions, and an electrolyte. The negativeelectrode comprises the above-described carbon material according to oneembodiment of the present invention or a carbon material produced by themethod according to one embodiment of the present invention.

The positive electrode comprises a current collector and a positiveelectrode active material layer on the current collector, the positiveelectrode active material layer comprising a positive electrode activematerial and a binder.

Examples of positive electrode active materials include metalchalcogenides, which are capable of occluding and releasing alkali metalcations, such as lithium ions, during charging and discharging. Examplesof metal chalcogenides include transition metal oxides, such as oxidesof vanadium, oxides of molybdenum, oxides of manganese, oxides ofchromium, oxides of titanium, and oxides of tungsten; transition metalsulfides, such as sulfides of vanadium, sulfides of molybdenum, sulfidesof titanium, and CuS; phosphorus-sulfur compounds of transition metals,such as NiPS₃ and FePS₃; selenium compounds of transition metals, suchas VSe₂ and NbSe₃; composite oxides of transition metals, such asFe_(0.25)V_(0.75)S₂ and Na_(0.1)CrS₂; and composite sulfides oftransition metals, such as LiCoS₂ and LiNiS₂.

Of these, from the viewpoint of occlusion and release of lithium ions,preferred are, for example, V₂O₅, V₅O₁₃, VO₂, Cr₂O₅, MnO₂, TiO₂, MoV₂O₈,LiCoO₂, LiNiO₂, LiMn₂O₄, TiS₂, V₂S₅, Cr_(0.55)V_(0.75)S₂, andCr_(0.5)V_(0.5)S₂, and particularly preferred are LiCoO₂, LiNiO₂,LiMn₂O₄, and lithium-transition metal composite oxides in which thesetransition metals are partially substituted with other metals. Thesepositive electrode active materials may be used alone or in combination.

For binding the positive electrode active material, any known binder canbe selected for use. Examples include inorganic compounds, such assilicates and water glass, and resins having no unsaturated bond, suchas Teflon (registered trademark) and polyvinylidene fluoride. Of these,resins having no unsaturated bond are preferred because they are lesslikely to decompose during oxidation reactions. Resins having anunsaturated bond, when used as resins for binding the positive electrodeactive material, may decompose during oxidation reactions. The weightaverage molecular weights of these resins are typically in the range of10,000 or greater, preferably 100,000 or greater, and typically3,000,000 or less, preferably 1,000,000 or less.

To the positive electrode active material layer, a conductive agent(conductive auxiliary) may be added to improve the conductivity of theelectrode. The conductive agent may be any conductive agent capable ofimparting conductivity when added in an appropriate amount to the activematerial, and typical examples include carbon powders, such as acetyleneblack, carbon black, and graphite powder, metal fibers, metal powders,and metal foils.

A positive plate is formed using a method similar to that for producinga negative electrode described above by slurrying the positive electrodeactive material and the binder with a solvent and applying the slurry toa current collector, followed by drying. Examples of raw materials ofthe current collector of the positive electrode include, but are notlimited to, aluminum, nickel, and stainless steel (SUS).

The electrolyte (also referred to as “electrolyte solution”) for use is,for example, a non-aqueous electrolyte solution of a lithium salt in anon-aqueous solvent, or a variant of the non-aqueous electrolytesolution formed into a gel, a rubber, or a solid sheet by adding amacromolecular organic compound or other compounds.

The non-aqueous solvent for use in the non-aqueous electrolyte solutionis not limited to a particular solvent, and it can be appropriatelyselected from known non-aqueous solvents that have been conventionallyused as solvents for non-aqueous electrolyte solutions. Examples includelinear carbonates, such as diethyl carbonate, dimethyl carbonate, andethyl methyl carbonate; cyclic carbonates, such as ethylene carbonate,propylene carbonate, and butylene carbonate; linear ethers, such as1,2-dimethoxyethane; cyclic ethers, such as tetrahydrofuran,2-methyltetrahydrofuran, sulfolane, and 1,3-dioxolane; linear esters,such as methyl formate, methyl acetate, and methyl propionate; andcyclic esters, such as γ-butyrolactone and γ-valerolactone.

Any one of these non-aqueous solvents may be used alone, or two or moreof these may be used in combination. In the case of a mixed solvent,preferred is a mixed solvent containing a cyclic carbonate and a linearcarbonate, and particularly preferred is a mixed solvent containingethylene carbonate and propylene carbonate as cyclic carbonates becausesuch a mixed solvent can provide high ion conductivity even at lowtemperatures to improve low-temperature charge load characteristics. Inparticular, the amount of propylene carbonate is preferably in the rangeof 2% by mass to 80% by mass, more preferably in the range of 5% by massto 70% by mass, still more preferably in the range of 10% by mass to 60%by mass, based on the total amount of non-aqueous solvent. Propylenecarbonate in an amount below this range reduces ion conductivity at lowtemperatures. Propylene carbonate in an amount above this range, when agraphite electrode is used, is solvated in lithium ions to penetratebetween graphite phases, thereby causing the graphite negative electrodeactive material to delaminate and degrade, which disadvantageouslyresults in an insufficient capacity.

The lithium salt for use in the non-aqueous electrolyte solution is alsonot limited to a particularly salt, and it can be appropriately selectedfrom known lithium salts known to be usable in this application.Examples include inorganic lithium salts, such as halides including LiCland LiBr, perhalogen acid salts including LiClO₄, LiBrO₄, and LiClO₄,and inorganic fluoride salts including LiPF₆, LiBF₄, and LiAsF₆; andfluorine-containing organic lithium salts, such asperfluoroalkanesulfonic acid salts including LiCF₃SO₃ and LiC₄F₉SO₃, andperfluoroalkanesulfonic imide salts including Litrifluoromethanesulfonyl imide ((CF₃SO₂)₂NLi). Of these, LiClO₄, LiPF₆,and LiBF₄ are preferred.

These lithium salts may be used alone or in a combination of two ormore. The concentration of lithium salts in the non-aqueous electrolytesolution is typically in the range of 0.5 mol/L to 2.0 mol/L.

When the non-aqueous electrolyte solution is used in the form of a gel,a rubber, or a solid sheet by incorporating a macromolecular organiccompound, specific examples of macromolecular organic compounds includemacromolecular polyether compounds, such as polyethylene oxide andpolypropylene oxide; cross-linked polymers of macromolecular polyethercompounds; macromolecular vinyl alcohol compounds, such as polyvinylalcohol and polyvinyl butyral; insolubilized macromolecular vinylalcohol compounds; polyepichlorohydrin; polyphosphazene; polysiloxane;macromolecular vinyl compounds, such as polyvinylpyrrolidone,polyvinylidene carbonate, and polyacrylonitrile; and polymer copolymers,such as poly(□-methoxyoligooxyethylene methacrylate),poly(□-methoxyoligooxyethylene methacrylate-co-methyl methacrylate), andpoly(hexafluoropropylene-vinylidene fluoride).

The non-aqueous electrolyte solution may further contain a film-formingagent. Specific examples of film-forming agents include carbonatecompounds, such as vinylene carbonate, vinyl ethyl carbonate, andmethylphenyl carbonate; alkene sulfides, such as ethylene sulfide andpropylene sulfide; sultone compounds, such as 1,3-propane sultone and1,4-butane sultone; and acid anhydrides, such as maleic anhydride andsuccinic anhydride. Furthermore, an overcharge inhibitor such asdiphenyl ether or cyclohexyl benzene may be added.

When these additives are used, the amount thereof is typically in therange of 10% by mass or less, preferably 8% by mass or less, morepreferably 5% by mass or less, particularly preferably 2% by mass orless, based on the total mass of the non-aqueous electrolyte solution.An excessive amount of these additives may have adverse effects onbattery characteristics, such as increases in initial irreversiblecapacity, degradation of low-temperature characteristics and ratecharacteristics, and other effects.

The electrolyte may also be a polymer solid electrolyte, which conductsalkali metal cations, such as lithium ions. Examples of polymer solidelectrolytes include solutions of lithium salts in the above-describedmacromolecular polyether compounds and polyether derivatives terminatedwith alkoxides in place of hydroxyl groups.

Typically, the positive electrode and the negative electrode areintervened by a porous separator, such as a porous membrane or anonwoven fabric, to prevent a short circuit between the electrodes. Inthis case, the porous separator is impregnated with the non-aqueouselectrolyte solution. Examples of raw materials of the separator includepolyolefins, such as polyethylene and polypropylene, andpolyethersulfone, and polyolefins are preferred.

The non-aqueous secondary battery may be of any type. Examples includecylindrical batteries including spirally-disposed sheet electrodes and aseparator, cylindrical batteries having an inside-out structurecombining pellet electrodes and a separator, and coin batteries in whichpellet electrodes and a separator are laminated. The batteries of thesetypes can be put in any desired outer case of any desired shape, such ascoins, cylinders, and prisms, and any desired size.

The non-aqueous secondary battery may be assembled in any appropriateprocedure depending on the battery structure. For example, a negativeelectrode is placed on an outer case; an electrolyte solution and aseparator are placed thereon; a positive electrode is placed oppositelyto the negative electrode; and these are caulked with a gasket and asealing plate to form a battery.

The carbon material for a non-aqueous secondary battery negativeelectrode of the present invention can provide a non-aqueous secondarybattery having high stability, a high output, a high capacity, a lowirreversible capacity, and a high cycle retention.

EXAMPLES

Specific embodiments of the present invention will now be described inmore detail with reference to examples, but these examples are notintended to limit the present invention.

The viscosity, contact angle, surface tension, and r cos θ ofgranulating agents were each measured by the methods described in thespecification.

First examples (Examples A) of the present invention will now bedescribed.

In Examples A, physical properties of carbon materials produced weremeasured by the following methods.

Preparation of Electrode Sheet

An electrode plate having an active material layer with an activematerial layer density of 1.60±0.03 g/cm³ was prepared using graphiteparticles of Examples or Comparative Examples. Specifically, 50.00±0.02g of a carbon material, 50.00±0.02 g (0.500 g on a solids basis) of a 1%by mass aqueous carboxymethylcellulose sodium salt solution, and1.00±0.05 g (0.5 g on a solids basis) of an aqueous dispersion of astyrene-butadiene rubber having a weight average molecular weight of270,000 were stirred with a Keyence hybrid mixer for 5 minutes, and themixture was defoamed for 30 seconds to give a slurry.

The slurry was applied to a 10-μm-thick copper foil, serving as acurrent collector, to a width of 10 cm using a small die coateravailable from Itochu Machining Co., Ltd. such that the carbon materialadhered in an amount of 12.00±0.3 mg/cm². The coated foil wasroll-pressed using a roller having a diameter of 20 cm to adjust thedensity of the active material layer to be 1.60±0.03 g/cm³, therebypreparing an electrode sheet.

Production of Non-Aqueous Secondary Battery (2016 Coin Battery)

The electrode sheet prepared by the above-described method was cut intoa disk having a diameter of 12.5 mm, and lithium metal foil was cut intoa disk having a diameter of 14 mm to prepare a counter electrode. Aseparator (made of a porous polyethylene film) was placed between thetwo electrodes, the separator being impregnated with an electrolytesolution of 1 mol/L of LiPF₆ in a mixed solvent of ethylene carbonateand ethyl methyl carbonate (volume ratio=3:7). In this manner, 2016 coinbatteries were produced.

Method of Producing Non-Aqueous Secondary Battery (Laminate Battery)

The electrode sheet prepared by the above-described method was cut to 4cm×3 cm to prepare a negative electrode, and a positive electrode madeof NMC was cut to the same area. The negative electrode and the positiveelectrode were combined with a separator (made of a porous polyethylenefilm) placed therebetween. An electrolyte solution of 1.2 mol/L of LiPF₆in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, anddimethyl carbonate (volume ratio=3:3:4) was injected in an amount of 250μL to produce a laminate battery.

Method for Measuring Discharge Capacity

Using the non-aqueous secondary battery (2016 coin battery) produced bythe above-described method, the capacity of the battery during chargingand discharging was measured by the following method.

The lithium counter electrode was charged to 5 mV at a current densityof 0.05 C and further charged at a constant voltage of 5 mV to a currentdensity of 0.005 C. The negative electrode was doped with lithium, andthen the lithium counter electrode was discharged to 1.5 V at a currentdensity of 0.1 C. Subsequently, a second charging and discharging wasperformed at the same current density. The discharge capacity at thesecond cycle was defined as a discharge capacity of this battery.

Low-Temperature Output Characteristics

Using the laminate non-aqueous electrolyte secondary battery produced bythe method for producing a non-aqueous electrolyte secondary batterydescribed above, low-temperature output characteristics were measured bythe following method.

A non-aqueous electrolyte secondary battery that had yet to go through acharge and discharge cycle was subjected to an initial charge anddischarge that involves three cycles in a voltage range of 4.1 V to 3.0V at 25° C. and a current of 0.2 C (1 C is a current at which a ratedcapacity at a 1-hour rate discharge capacity is discharged in 1 hour,and so on) and two cycles in a voltage range of 4.2 V to 3.0 V at acurrent of 0.2 C (in charging, a constant-voltage charge at 4.2 V wasfurther performed for 2.5 hours).

Furthermore, charging was performed at a current of 0.2 C to an SOC of50%, and then constant-current discharging was performed in alow-temperature environment at −30° C. for 2 seconds at varying currentsof ⅛ C, ¼ C, ½ C, 1.5 C, and 2 C. The battery voltage drop at 2 secondsafter discharging under each condition was measured. From eachmeasurement, a current I that could be passed in 2 seconds when theupper limit charge voltage was 3 V was calculated, and a valuecalculated from the formula: 3×I (W) was defined as the low-temperatureoutput characteristics of each battery.

d50

The d50 was determined as a volume-based median diameter by suspending0.01 g of a carbon material in 10 mL of a 0.2% by mass aqueous solutionof a polyoxyethylene sorbitan monolaurate surfactant (Tween 20(registered trademark)), placing the suspension (a measurement sample)in a commercially available laser diffraction/scattering particle sizedistribution analyzer (e.g., LA-920 available from HORIBA, Ltd.),irradiating the measurement sample with ultrasonic waves of 28 kHz at apower of 60 W for 1 minute, and then performing a measurement with theanalyzer.

Mode Pore Diameter (PD) in Pore Diameter Range of 0.01 μm to 1 μm, HalfWidth at Half Maximum of Pore Distribution (Log (Nm)), Cumulative PoreVolume at Pore Diameters in Range of 0.01 μm to 1 μm, and Total PoreVolume

The measurement by mercury intrusion was carried out using a mercuryporosimeter (Autopore 9520 available from Micromeritics Corp). Around0.2 g of a sample (carbon material) was weighed into a powder cell, andthe cell was sealed. The cell was subjected to a degassing pretreatmentat room temperature under vacuum (50 μmHg or lower) for 10 minutes, andthen the pressure in the cell was reduced stepwise to 4 psia. Mercurywas introduced into the cell, and the pressure was increased stepwisefrom 4 psia to 40,000 psia and then reduced to 25 psia. From the mercuryintrusion curve obtained, a pore distribution was calculated using theWashburn equation. The calculation was made assuming that the surfacetension of mercury was 485 dyne/cm, and the contact angle of mercury was140°.

From the pore distribution obtained, a mode pore diameter (PD) in a porediameter range of 0.01 μm to 1 μm, a cumulative pore volume at porediameters in a range of 0.01 μm to 1 μm, and a total pore volume werecalculated. The half width at half maximum of pore distribution (log(nm)) is defined as a half width at half maximum at a micropore side ofa peak in a pore diameter range of 0.01 μm to 1 μm in the poredistribution (nm) with the horizontal axis expressed in common logarithm(log (nm)).

Roundness (Average Roundness)

Using a flow-type particle image analyzer (FPIA-2000 available fromSysmex Corporation), a particle size distribution based on equivalentcircle diameter was measured, and a roundness was determined.Ion-exchanged water was used as a dispersion medium, and polyoxyethylene(20) monolaurate was used as a surfactant. The equivalent circlediameter is a diameter of a circle (equivalent circle) having the sameprojected area as that of a captured particle image, and the roundnessis a ratio of the perimeter of the equivalent circle, as the numerator,to the perimeter of the captured particle projection image, as thedenominator. Roundnesses of particles having an equivalent diameter inthe range of 1.5 to 40 μm were averaged to determine the roundness.

Frequency of Particles of 3 μm or Less

The frequency of particles with a particle diameter of 3 μm or less wasdetermined by mixing 50 mL of a 0.2% by volume aqueous solution of apolyoxyethylene sorbitan monolaurate surfactant (Tween 20 (registeredtrademark)) with 0.2 g of a carbon material, applying ultrasonic wavesof 28 kHz at a power of 60 W for 5 minutes using a flow-type particleimage analyzer “FPIA-2000 available from Sysmex Industrial Corp.”, andthen counting the number of particles with a detection range set to 0.6to 400 μm.

Tap Density

Using a powder density meter, the carbon material of the presentinvention was dropped through a sieve with openings of 300 μm into acylindrical tap cell with a diameter of 1.6 cm and a volume capacity of20 cm³ to fill up the cell, and then a tap with a stroke length of 10 mmwas given 1,000 times. The density calculated from the volume at thistime and the mass of the sample was defined as the tap density.

Specific Surface Area (SA)

The BET specific surface area was defined as a value determined asfollows: using a surface area meter (e.g., a Gemini 2360 specificsurface area analyzer available from Shimadzu Corporation), a carbonmaterial sample was preliminarily vacuum dried under a nitrogen streamat 100° C. for 3 hours and then cooled to liquid nitrogen temperature,and using a nitrogen-helium mixed gas precisely regulated so as to havea nitrogen pressure of 0.3 relative to atmospheric pressure, a BETspecific surface area was measured by a nitrogen adsorption BETmultipoint method according to a flowing gas method.

Example A1

A flake natural graphite having a d50 of 100 μm was crushed with amechanical crusher having a crushing rotor and a liner to give a flakenatural graphite having a d50 of 30 μm and a water content of 0.03% bymass. To 100 g of the resulting flake natural graphite, 6 g of agranulating agent of a paraffinic oil (liquid paraffin available fromWako Pure Chemical Industries, Ltd., first grade, physical properties at25° C.: viscosity=95 cP, contact angle=13.2°, surface tension=31.7 mN/m,r cos θ=30.9) was added and mixed with stirring. The sample obtained wasdisintegrated and mixed using a hammer mill (MF10 available from IKA) ata rotation speed of 3,000 rpm to give a flake natural graphite to whichthe granulating agent uniformly adhered. Using a Model NHS-1hybridization system available from Nara Machinery Co., Ltd., the flakenatural graphite to which the granulating agent uniformly adhered wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes while fine powder generated during the spheroidization wasdeposited on the base material and incorporated into the spheroidizedparticles, and heat treated in an inert gas at 720° C. to give aspheroidized natural graphite having a d50 of 19.4 μm. Using themeasurement methods described above, d50, Tap (tap density), specificsurface area, pore diameter, pore volume, roundness, pore distribution,frequency of particles, discharge capacity, and low-temperature outputcharacteristics were measured. The results are shown in Tables 1A and2A.

Comparative Example A1

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 3minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite fine powder not deposited on the base materialor incorporated into the spheroidized particles. This sample wasclassified to remove the flake graphite fine powder, thereby providing aspheroidized graphite having a d50 of 19.5 μm. The results of themeasurements made in the same manner as in Example A1 are shown inTables 1A and 2A.

Comparative Example A2

The sample obtained in Comparative Example A1 was further mechanicallyspheroidized at a rotor peripheral speed of 85 m/sec for 3 minutes usinga Model NHS-1 hybridization system available from Nara Machinery Co.,Ltd. In the sample obtained was confirmed the presence of a large amountof flake graphite fine powder not deposited on the base material orincorporated into the spheroidized particles. This sample was classifiedto remove the flake graphite fine powder, thereby providing aspheroidized graphite having a d50 of 19.3 μm. The results of themeasurements made in the same manner as in Example A1 are shown inTables 1A and 2A.

Example A2

The spheroidized natural graphite before heat treatment obtained inExample A1 and a coal-tar pitch, serving as an amorphous carbonprecursor, were mixed and heat treated in an inert gas at 1,300° C., andthen the burned product was disintegrated and classified to give amulti-layered carbon material made of graphite particles and anamorphous carbon combined with each other. The burning yield showed thatthe mass ratio of spheroidized graphite particle to amorphous carbon(spheroidized graphite particle/amorphous carbon) of the multi-layeredcarbon material was 1:0.03. The results of the measurements made in thesame manner as in Example A1 are shown in Tables 1A and 2A.

Example A3

A multi-layered carbon material made of graphite particles and anamorphous carbon combined with each other was obtained in the samemanner as in Example A2 except that the mass ratio of spheroidizedgraphite particle to amorphous carbon (spheroidized graphiteparticle/amorphous carbon) was 1:0.065. The results of the measurementsmade in the same manner as in Example A1 are shown in Tables 1A and 2A.

Comparative Example A3

The spheroidized natural graphite obtained in Comparative Example A2 anda coal-tar pitch, serving as an amorphous carbon precursor, were mixedand heat treated in an inert gas at 1,300° C., and then the burnedproduct was disintegrated and classified to give a multi-layered carbonmaterial made of graphite particles and an amorphous carbon combinedwith each other. The burning yield showed that the mass ratio ofspheroidized graphite particle to amorphous carbon (spheroidizedgraphite particle/amorphous carbon) of the multi-layered carbon materialwas 1:0.03. The results of the measurements made in the same manner asin Example A1 are shown in Tables 1A and 2A.

Example A4

A flake natural graphite having a d50 of 100 μm was crushed with a dryair-flow crusher to give a flake natural graphite having a d50 of 6 μm,a Tap of 0.13 g/cm³, and a water content of 0.08% by mass. To 100 g ofthe resulting flake natural graphite, 12 g of a granulating agent of aparaffinic oil (liquid paraffin available from Wako Pure ChemicalIndustries, Ltd., first grade, physical properties at 25° C.:viscosity=95 cP, contact angle=13.2°, surface tension=31.7 mN/m, r cosθ=30.9) was added and mixed with stirring. The sample obtained wasdisintegrated and mixed using a hammer mill (MF10 available from IKA) ata rotation speed of 3,000 rpm to give a flake natural graphite to whichthe granulating agent uniformly adhered. Using a Model NHS-1hybridization system available from Nara Machinery Co., Ltd., the flakenatural graphite to which the granulating agent uniformly adhered wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes while fine powder generated during the spheroidization wasdeposited on the base material and incorporated into the spheroidizedparticles, and heat treated in an inert gas at 720° C. to give aspheroidized graphite having a d50 of 9.2 μm. The results of themeasurements made in the same manner as in Example A1 are shown inTables 1A and 2A.

Example A5

A flake natural graphite having a d50 of 100 μm was crushed with a dryswirl-flow crusher to give a flake natural graphite having a d50 of 6μm, a Tap of 0.38 g/cm³, and a water content of 0.08% by mass. To 100 gof the resulting flake natural graphite, 12 g of a granulating agent ofa paraffinic oil (liquid paraffin available from Wako Pure ChemicalIndustries, Ltd., first grade, physical properties at 25° C.:viscosity=95 cP, contact angle=13.2°, surface tension=31.7 mN/m, r cosθ=30.9) was added and mixed with stirring. The sample obtained wasdisintegrated and mixed using a hammer mill (MF10 available from IKA) ata rotation speed of 3,000 rpm to give a flake natural graphite to whichthe granulating agent uniformly adhered. Using a Model NHS-1hybridization system available from Nara Machinery Co., Ltd., the flakenatural graphite to which the granulating agent uniformly adhered wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes while fine powder generated during the spheroidization wasdeposited on the base material and incorporated into the spheroidizedparticles, and heat treated in an inert gas at 720° C. to give aspheroidized graphite having a d50 of 9.9 μm. The results of themeasurements made in the same manner as in Example A1 are shown inTables 1A and 2A.

Comparative Example A4

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite fine powder not deposited on the base materialor incorporated into the spheroidized particles. This sample wasclassified to remove the flake graphite fine powder, thereby providing aspheroidized graphite having a d50 of 10.8 μm. The results of themeasurements made in the same manner as in Example A1 are shown inTables 1A and 2A.

Comparative Example A5

A flake natural graphite having a d50 of 100 μm was spheroidized andthen classified to remove the above-described flake graphite finepowder. The spheroidized graphite obtained by spheroidizing the flakegraphite was isotropically pressurized to give a spheroidized naturalgraphite having a cumulative pore volume at pore diameters of 0.01 μm to1 μm of 0.069. After that, the spheroidized natural graphite and acoal-tar pitch, serving as an amorphous carbon precursor, were mixed andheat treated in an inert gas at 1,300° C., and then the burned productwas disintegrated and classified to give a multi-layered carbon materialmade of graphite particles and an amorphous carbon combined with eachother. The burning yield showed that the mass ratio of spheroidizedgraphite particle to amorphous carbon (spheroidized graphiteparticle/amorphous carbon) of the multi-layered carbon material was1:0.03. The results of the measurements made in the same manner as inExample A1 are shown in Tables 1A and 2A.

Example A6

A flake natural graphite having a d50 of 100 μm was crushed with a dryswirl-flow crusher to give a flake natural graphite having a d50 of 8.1μm, a Tap of 0.39 g/cm³, and a water content of 0.08% by mass. To 100 gof the resulting flake natural graphite, 12 g of a granulating agent ofa paraffinic oil (liquid paraffin available from Wako Pure ChemicalIndustries, Ltd., first grade, physical properties at 25° C.:viscosity=95 cP, contact angle=13.2°, surface tension=31.7 mN/m, r cosθ=30.9) was added and mixed with stirring. The sample obtained wasdisintegrated and mixed using a hammer mill (MF10 available from IKA) ata rotation speed of 3,000 rpm to give a flake natural graphite to whichthe granulating agent uniformly adhered. Using a Model NHS-1hybridization system available from Nara Machinery Co., Ltd., the flakenatural graphite to which the granulating agent uniformly adhered wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes while fine powder generated during the spheroidization wasdeposited on the base material and incorporated into the spheroidizedparticles, and heat treated in an inert gas at 720° C. to give aspheroidized graphite having a d50 of 12.9 μm. The results of themeasurements made in the same manner as in Example A1 are shown inTables 1A and 2A.

Example A7

The spheroidized natural graphite before heat treatment obtained inExample A6 and a coal-tar pitch, serving as an amorphous carbonprecursor, were mixed and heat treated in an inert gas at 1,300° C., andthen the burned product was disintegrated and classified to give amulti-layered carbon material made of graphite particles and anamorphous carbon combined with each other. The burning yield showed thatthe mass ratio of spheroidized graphite particle to amorphous carbon(spheroidized graphite particle/amorphous carbon) of the multi-layeredcarbon material was 1:0.065. The results of the measurements made in thesame manner as in Example A1 are shown in Tables 1A and 2A.

Example A8

The spheroidized natural graphite before heat treatment obtained inExample A6 and a coal-tar pitch, serving as an amorphous carbonprecursor, were mixed and heat treated in an inert gas at 1,300° C., andthen the burned product was disintegrated and classified to give amulti-layered carbon material made of graphite particles and anamorphous carbon combined with each other. The burning yield showed thatthe mass ratio of spheroidized graphite particle to amorphous carbon(spheroidized graphite particle/amorphous carbon) of the multi-layeredcarbon material was 1:0.08. The results of the measurements made in thesame manner as in Example A1 are shown in Tables 1A and 2A.

Comparative Example A6

The spheroidized natural graphite obtained in Comparative Example A4 anda coal-tar pitch, serving as an amorphous carbon precursor, were mixedand heat treated in an inert gas at 1,300° C., and then the burnedproduct was disintegrated and classified to give a multi-layered carbonmaterial made of graphite particles and an amorphous carbon combinedwith each other. The burning yield showed that the mass ratio ofspheroidized graphite particle to amorphous carbon (spheroidizedgraphite particle/amorphous carbon) of the multi-layered carbon materialwas 1:0.065. The results of the measurements made in the same manner asin Example A1 are shown in Tables 1A and 2A.

TABLE 1A Frequency of Particles Comulative Intra- Having Pore ParticlePore Volume at Half Diameter Pore Total Width at of 3 μm Diameters Pored50, Tap, SA, PD, PD/50, Half or to 1 μm, Volume, μm g/cm³ Roundnessm²/g μm % Maximum less, % ml ml Example A1 19.4 1.06 0.93 13.4 0.22 1.110.71 51 0.11 0.76 Comparative 19.5 0.90 0.91 4.9 0.67 3.44 0.42 64 0.140.57 Example A1 Comparative 19.3 1.08 0.94 6.3 0.43 2.24 0.41 66 0.120.56 Example A2 Example A2 18.4 1.19 0.93 5.6 0.22 1.19 0.46 — 0.09 0.47Example A3 20.0 1.20 0.93 4.1 0.22 1.09 0.38 — 0.10 0.48 Comparative19.2 1.19 0.94 2.79 0.44 2.29 0.26 — 0.10 0.47 Example A3 Example A4 9.20.77 0.92 15.0 0.09 0.99 0.24 20 0.19 0.88 Example A5 9.9 0.91 0.93 21.30.06 0.64 0.21 13 0.16 0.78 Comparative 10.8 0.93 0.93 8.8 0.22 2.030.35 44 0.13 0.65 Example A4 Comparative 21.9 1.20 0.92 8.8 — — — —<0.069 <0.54 Example A5 Example A6 12.9 0.88 0.93 15.3 0.11 0.84 0.28 160.13 0.67 Example A7 12.0 1.05 0.93 7.9 0.11 0.91 0.25 — 0.12 0.62Example A8 11.8 1.02 0.93 7.1 0.11 0.92 0.26 — 0.11 0.67 Comparative11.4 1.04 0.92 3.1 0.54 4.77 0.33 — 0.11 0.63 Example A6

TABLE 2A Low-Temperature Output Characteristics, Discharge (ComparativeCapacity, Example A1 = mAh/g 100) Example A1 367 122 Comparative 368 100Example A1 Comparative 368 104 Example A2 Example A2 362 132 Example A3363 126 Comparative 366 108 Example A3 Example A4 365 128 Example A5 362172 Comparative 365 118 Example A4 Comparative 362 91 Example A5 ExampleA6 365 128 Example A7 362 142 Example A8 359 151 Comparative 362 103Example A6

In Examples A1 to A8, the flake natural graphite adjusted to have aprescribed particle size was spheroidized while fine powder generatedduring the spheroidization was deposited on the base material and/orincorporated into the spheroidized particles, whereby a PD/d50(%) in theprescribed range was successfully achieved to provide a high capacityand excellent low-temperature output characteristics. By contrast, inComparative Examples A1 to A4 and A6, where the PD/d50(%) was outsidethe prescribed range, and Comparative Example A5, where the cumulativepore volume in a range of 0.01 μm to 1 μm was outside the prescribedrange, degraded low-temperature output characteristics were provided.

Second examples (Examples B) of the present invention will now bedescribed. In Examples B, physical properties of carbon materialsproduced were measured by the following methods.

d50

The d50 was determined as a volume-based median diameter by suspending0.01 g of a carbon material in 10 mL of a 0.2% by mass aqueous solutionof a polyoxyethylene sorbitan monolaurate surfactant (Tween 20(registered trademark)), placing the suspension (a measurement sample)in a commercially available laser diffraction/scattering particle sizedistribution analyzer (e.g., LA-920 available from HORIBA, Ltd.),irradiating the measurement sample with ultrasonic waves of 28 kHz at apower of 60 W for 1 minute, and then performing a measurement with theanalyzer.

Tap Density

Using a powder density meter, the carbon material was dropped through asieve with openings of 300 μm into a cylindrical tap cell with adiameter of 1.6 cm and a volume capacity of 20 cm³ to fill up the cell,and then a tap with a stroke length of 10 mm was given 1,000 times. Thedensity calculated from the volume at this time and the mass of thesample was defined as the tap density.

Specific Surface Area SA

The specific surface area SA was defined as a value determined asfollows: using a surface area meter (Gemini 2360 specific surface areaanalyzer available from Shimadzu Corporation), a carbon material samplewas preliminarily vacuum dried under a nitrogen stream at 100° C. for 3hours and then cooled to liquid nitrogen temperature, and using anitrogen-helium mixed gas precisely regulated so as to have a nitrogenpressure of 0.3 relative to atmospheric pressure, a BET specific surfacearea was measured by a nitrogen adsorption BET multipoint methodaccording to a flowing gas method.

Residual Carbon Ratio of Granulating Agent

Sample weights before and after heat treatment of a granulating agent inan inert atmosphere at 700° C. for 1 hour were measured, and theresidual carbon ratio of the granulating agent was calculated by thefollowing formula.

Residual carbon ratio (% by mass) of granulating agent=[w2/w1]×100

(w1 is a mass (g) of a granulating agent before heat treatment, and w2is a mass (g) of the granulating agent after heat treatment)

Example B1

A flake natural graphite having a d50 of 100 μm was crushed with a dryswirl-flow crusher to give a flake natural graphite having a d50 of 8.1μm, a Tap of 0.39 g/cm³, and a water content of 0.08% by mass. To 100 gof the resulting flake natural graphite, 9 g of a granulating agent ofN-methyl-2-pyrrolidone (NMP) (Wako Pure Chemical Industries, Ltd.,special grade; flash point, 86° C.) was added and mixed with stirring.The sample obtained was disintegrated and mixed using a hammer mill(MF10 available from IKA) at a rotation speed of 3,000 rpm to give aflake natural graphite to which the granulating agent uniformly adhered.Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., the sample obtained was mechanically spheroidized at a rotorperipheral speed of 85 m/sec for 10 minutes. The sample obtained washeat treated in a nitrogen atmosphere at 700° C. to give a spheroidizedgraphite sample from which the granulating agent was removed. Using themeasurement methods described above, the residual carbon ratio,viscosity, contact angle with graphite, and surface tension of thegranulating agent were measured, and the d50, d10, d90, SA, and Tap ofthe sample obtained were measured. The results are shown in Table 1B.

Example B2

A sample was prepared in the same manner as in Example B1 except that 12g of a granulating agent of NMP (Wako Pure Chemical Industries, Ltd.,special grade; flash point, 86° C.) was added. The results of themeasurements made in the same manner as in Example B1 are shown in Table1B.

Example B3

A sample was prepared in the same manner as in Example B1 except that 15g of a granulating agent of NMP (Wako Pure Chemical Industries, Ltd.,special grade; flash point, 86° C.) was added. The results of themeasurements made in the same manner as in Example B1 are shown in Table1B.

Example B4

A sample was prepared in the same manner as in Example B1 except that 12g of a granulating agent of a solution of 3% by mass methyl methacrylatepolymer (PMMA) (Wako Pure Chemical Industries, Ltd.) in NMP (Wako PureChemical Industries, Ltd., special grade; flash point, 86° C.) wasadded. The results of the measurements made in the same manner as inExample B1 are shown in Table 1B.

Example B5

A sample was prepared in the same manner as in Example B1 except that 12g of a granulating agent of a solution of 10% by mass PMMA (Wako PureChemical Industries, Ltd.) in NMP (Wako Pure Chemical Industries, Ltd.,special grade; flash point, 86° C.) was added. The results of themeasurements made in the same manner as in Example B1 are shown in Table1B.

Example B6

A sample was prepared in the same manner as in Example B1 except that 12g of a granulating agent of a solution of 15% by mass PMMA (Wako PureChemical Industries, Ltd.) in NMP (Wako Pure Chemical Industries, Ltd.,special grade; flash point, 86° C.) was added. The results of themeasurements made in the same manner as in Example B1 are shown in Table1B.

Example B7

A sample was prepared in the same manner as in Example B1 except that 12g of a granulating agent of pure water was added. The results of themeasurements made in the same manner as in Example B1 are shown in Table1B.

Example B8

A sample was prepared in the same manner as in Example B1 except that 12g of a granulating agent of an aqueous solution of 10% by masspolyacrylic acid ammonium (PAANH₃) (Wako Pure Chemical Industries, Ltd.,first grade) was added. The results of the measurements made in the samemanner as in Example B1 are shown in Table 1B.

Example B9

A sample was prepared in the same manner as in Example B1 except that 12g of a granulating agent of an aqueous solution of 30% by masspolyacrylic acid ammonium (PAANH₃) (Wako Pure Chemical Industries, Ltd.,first grade) was added. The results of the measurements made in the samemanner as in Example B1 are shown in Table 1B.

Example B10

A sample was prepared in the same manner as in Example B1 except that 12g of a granulating agent of an aqueous solution of 44% by mass PAANH₃(Wako Pure Chemical Industries, Ltd., first grade) was added. Theresults of the measurements made in the same manner as in Example B1 areshown in Table 1B.

Example B11

A sample was prepared in the same manner as in Example B1 except that 15g of a granulating agent of coal tar (flash point, 70° C.) was added.Since the viscosity of the coal tar was 500 cP or more at 25° C., thecontact angle was measured in accordance with the measurement methoddescribed above after the sample was heated to 60° C. to decrease theviscosity to 500 cP or lower. The other properties were measured in thesame manner as in Example B1. The results are shown in Table 1B.

Example B12

A sample was prepared in the same manner as in Example B1 except that 9g of a granulating agent of creosote oil (flash point, 70° C.) wasadded. The results of the measurements made in the same manner as inExample B1 are shown in Table 1B.

Example B13

A sample was prepared in the same manner as in Example B1 except that 12g of a granulating agent of creosote oil was added. The results of themeasurements made in the same manner as in Example B1 are shown in Table1B.

Example B14

A sample was prepared in the same manner as in Example B1 except that 15g of a granulating agent of creosote oil was added. The results of themeasurements made in the same manner as in Example B1 are shown in Table1B.

Example B15

A sample was prepared in the same manner as in Example B1 except that 9g of a granulating agent of a paraffinic oil (liquid paraffin availablefrom Wako Pure Chemical Industries, Ltd., first grade; flash point, 238°C.; aniline point, >100° C.) was added. The results of the measurementsmade in the same manner as in Example B1 are shown in Table 1B.

Example B16

A sample was prepared in the same manner as in Example B1 except that 12g of a granulating agent of a paraffinic oil (liquid paraffin availablefrom Wako Pure Chemical Industries, Ltd., first grade; flash point, 238°C.; aniline point, >100° C.) was added. The results of the measurementsmade in the same manner as in Example B1 are shown in Table 1B.

Example B17

A sample was prepared in the same manner as in Example B1 except that 15g of a granulating agent of a paraffinic oil (liquid paraffin availablefrom Wako Pure Chemical Industries, Ltd., first grade; flash point, 238°C.; aniline point, >100° C.) was added. The results of the measurementsmade in the same manner as in Example B1 are shown in Table 1B.

Example B18

A sample was prepared in the same manner as in Example B1 except that 9g of a granulating agent of an aromatic oil (1) (flash point, 242° C.;aniline point, 29° C.; containing a naphthalene ring structure in itsmolecule) was added. The results of the measurements made in the samemanner as in Example B1 are shown in Table 1B.

Example B19

A sample was prepared in the same manner as in Example B1 except that 12g of a granulating agent of the aromatic oil (1) (flash point, 242° C.;aniline point, 29° C.; containing a naphthalene ring structure in itsmolecule) was added. The results of the measurements made in the samemanner as in Example B1 are shown in Table 1B.

Example B20

A sample was prepared in the same manner as in Example B1 except that 15g of a granulating agent of the aromatic oil (1) (flash point, 242° C.;aniline point, 29° C.; containing a naphthalene ring structure in itsmolecule) was added. The results of the measurements made in the samemanner as in Example B1 are shown in Table 1B.

Example B21

A sample was prepared in the same manner as in Example B1 except that 9g of a granulating agent of an aromatic oil (2) (flash point, 150° C.;aniline point, none; mixed aniline point, 15° C.; containing a benzenering structure in its molecule) was added. The results of themeasurements made in the same manner as in Example B1 are shown in Table1B.

Example B22

A sample was prepared in the same manner as in Example B1 except that 12g of a granulating agent of the aromatic oil (2) (flash point, 150° C.;aniline point, none; mixed aniline point, 15° C.; containing a benzenering structure in its molecule) was added. The results of themeasurements made in the same manner as in Example B1 are shown in Table1B.

Example B23

A sample was prepared in the same manner as in Example B1 except that 15g of a granulating agent of the aromatic oil (2) (flash point, 150° C.;aniline point, none; mixed aniline point, 15° C.; containing a benzenering structure in its molecule) was added. The results of themeasurements made in the same manner as in Example B1 are shown in Table1B.

Comparative Example B1

A sample was prepared in the same manner as in Example B1 except that nogranulating agent was added. The results of the measurements made in thesame manner as in Example B1 are shown in Table 1B.

Comparative Example B2

A sample was prepared in the same manner as in Example B1 except that 12g of a granulating agent of coal-tar pitch (softening point, 90° C.;being solid during granulation) was added. The results of themeasurements made in the same manner as in Example B1 are shown in Table1B.

Comparative Example B3

A sample was prepared in the same manner as in Example B1 except that 12g of an organic compound of PMMA (Wako Pure Chemical Industries, Ltd.;melting point, 105° C.; being solid during granulation) was added. Theresults of the measurements made in the same manner as in Example B1 areshown in Table 1B.

Comparative Example B4

The sample obtained in Comparative Example B1 was air classified toremove the flake graphite fine powder that had not been granulated togive a spheroidized graphite having a d50 of 10.9 μm and a Tap densityof 0.88 g/cm³. The results of the measurements made in the same manneras in Example B1 are shown in Table 1B.

TABLE 1B Residual Viscosity, Contact Surface Amount of GranulatingCarbon cP Angle θ, ° Tension γ, Granulating d10, d50, d50, Tap, SA,Agent Ratio, % (25° C.) (25° C.) mN/m (25° C.) γcosθ Agent, g μm μm μmg/cm³ m²/g Example B1 NMP 0 1.9 4.4 40.8 40.7 9 6.6 10.4 15.7 0.92 15.8Example B2 12 7.5 11.3 17.1 0.91 16.0 Example B3 15 6.7 10.6 16.0 0.8916.4 Example B4 3% PMMA in 0 6.2 7.3 41.0 40.6 12 7.8 11.7 17.3 0.9216.6 NMP solution Example B5 10% PMMA in 0 43 9.7 41.3 40.7 12 8.1 12.117.9 0.92 16.6 NMP solution Example B6 15% PMMA in 0 164 13.1 41.7 40.612 9.0 14.1 22.6 0.96 17.4 NMP solution Example B7 Pure water 0 0.9 95.572.1 −6.9 12 2.9 6.9 12.6 0.76 11.2 Example B8 Aqueous solution 1.5 3.994.8 72.9 −6.1 12 3.9 8.0 13.3 0.87 10.3 of 10% PAANH3 Example B9Aqueous solution 4.4 32 88.1 75.8 2.5 12 6.5 11.1 18.1 1.00 11.4 of 30%PAANH3 Example B10 Aqueous solution 6.5 169 83.8 78.6 8.5 12 5.5 10.820.4 1.00 13.2 of 44% PAANH3 Example B11 Coal tar 27 6030 20.8 (60° C.)37.6 35.1 15 7.8 12.9 22.1 0.93 11.9 Example B12 Creosote oil 0.4 5.010.8 39.4 38.7 9 7.0 10.8 16.2 0.94 15.4 Example B13 12 8.0 11.9 17.70.94 15.3 Example B14 15 8.2 12.3 18.1 0.89 15.2 Example B15 Paraffinicoil 0 90 13.2 31.7 30.9 9 7.5 11.4 17.0 0.85 15.1 Example B16 12 8.412.5 18.3 0.86 15.9 Example B17 15 9.5 14.7 24.1 0.88 18.5 Example B18Aromatic oil (1) 0 58 12.9 33.7 32.8 9 7.5 11.4 17.0 0.92 15.9 ExampleB19 12 8.2 12.4 18.6 0,92 16.3 Example B20 15 9.4 14.3 22.4 0.92 17.9Example B21 Aromatic oil (2) 0 8.4 11.4 36.4 35.7 9 7.1 10.8 15.9 0.9215.5 Example B22 12 7.8 11.5 16.7 0.90 15.5 Example B23 15 7.7 12.0 18.30.81 15.1 Comparative — — — — — — 0 2.7 6.5 12.1 0.79 12.7 Example B1Comparative Coal-tar pitch 40 — — — — 12 4.8 9.7 17.2 0.71 7.4 ExampleB2 Comparative PMMA 0 — — — — 12 2.9 6.8 12.6 0.73 12.1 Example B3Comparative — — — — — — 0 6.8 10.9 17.3 0.88 8.4 Example B4

In Examples B1 to B23, the flake natural graphite adjusted to have asuitable particle size was spheroidized with a granulating agent havingprescribed physical properties added, as a result of which thegranulation spheroidization was promoted to reduce the amount of flakegraphite fine powder generated, leading to increases in d10 and d50.Furthermore, the spheroidization improved particle-filling properties,leading to increases in Tap density.

By contrast, in Comparative Examples B1 and B4, where the flake naturalgraphite was spheroidized with no granulating agent added, andComparative Examples B2 and B3, where the spheroidization was carriedout with a granulating agent not satisfying the requirements added, theflake natural graphites poorly adhered to each other, and thus thegranulation spheroidization was not sufficiently promoted, leading toinsufficient increases in d50 and Tap.

Batteries produced using the carbon materials of Example B16 andComparative Example B4 were evaluated by the following method. Theresults are shown in Table 2B.

Preparation of Electrode Sheet

An electrode plate having an active material layer with an activematerial layer density of 1.60±0.03 g/cm³ or 1.35±0.03 g/cm³ wasprepared using a carbon material of Examples or Comparative Examples.Specifically, 50.00±0.02 g of a carbon material, 50.00±0.02 g (0.500 gon a solids basis) of a 1% by mass carboxymethylcellulose sodium saltaqueous solution, and 1.00±0.05 g (0.5 g on a solids basis) of anaqueous dispersion of a styrene-butadiene rubber having a weight averagemolecular weight of 270,000 were stirred with a Keyence hybrid mixer for5 minutes, and the mixture was defoamed for 30 seconds to give a slurry.

The slurry was applied to a 10-μm-thick copper foil, serving as acurrent collector, to a width of 10 cm using a small die coateravailable from Itochu Machining Co., Ltd. such that the carbon materialadhered in an amount of 12.00±0.3 mg/cm² or 6.00±0.3 mg/cm². The coatedfoil was roll-pressed using a roller having a diameter of 20 cm toadjust the density of the active material layer to be 1.60±0.03 g/cm³ or1.35±0.03 g/cm³, thereby preparing an electrode sheet.

Production of Non-Aqueous Secondary Battery (2016 Coin Battery)

The electrode sheet prepared by the above-described method, to which thecarbon material adhered in an amount of 12.00±0.3 mg/cm² and in whichthe density of the active material layer was adjusted to be 1.60±0.03g/cm³, was cut into a disk having a diameter of 12.5 mm, and lithiummetal foil was cut into a disk having a diameter of 14 mm to prepare acounter electrode. A separator (made of a porous polyethylene film) wasplaced between the two electrodes, the separator being impregnated withan electrolyte solution of 1 mol/L of LiPF₆ in a mixed solvent ofethylene carbonate and ethyl methyl carbonate (volume ratio=3:7). Inthis manner, 2016 coin batteries were produced.

Method of Producing Non-Aqueous Secondary Battery (Laminate Battery)

The electrode sheet prepared by the above-described method, to which thecarbon material adhered in an amount of 6.00±0.3 mg/cm² and in which thedensity of the active material layer was adjusted to be 1.35±0.03 g/cm³,was cut to 4 cm×3 cm to prepare a negative electrode, and a positiveelectrode made of NMC was cut to the same area. The negative electrodeand the positive electrode were combined with a separator (made of aporous polyethylene film) placed therebetween. An electrolyte solutionof 1.2 mol/L of LiPF₆ in a mixed solvent of ethylene carbonate, ethylmethyl carbonate, and dimethyl carbonate (volume ratio=3:3:4) wasinjected in an amount of 200 μL to produce a laminate battery.

Method for Measuring Discharge Capacity

Using the non-aqueous secondary battery (2016 coin battery) produced bythe above-described method, the capacity of the battery during chargingand discharging was measured by the following method.

The lithium counter electrode was charged to 5 mV at a current densityof 0.05 C and further charged at a constant voltage of 5 mV to a currentdensity of 0.005 C. The negative electrode was doped with lithium, andthen the lithium counter electrode was discharged to 1.5 V at a currentdensity of 0.1 C. The discharge capacity at this time was defined as adischarge capacity of this battery.

Low-Temperature Output Characteristics

Using the laminate non-aqueous electrolyte secondary battery produced bythe method for producing a non-aqueous electrolyte secondary batterydescribed above, low-temperature output characteristics were measured bythe following method.

A non-aqueous electrolyte secondary battery that had yet to go through acharge and discharge cycle was subjected to an initial charge anddischarge that involves three cycles in a voltage range of 4.1 V to 3.0V at 25° C. and a current of 0.2 C (1 C is a current at which a ratedcapacity at a 1-hour rate discharge capacity is discharged in 1 hour,and so on) and two cycles in a voltage range of 4.2 V to 3.0 V at acurrent of 0.2 C (in charging, a constant-voltage charge at 4.2 V wasfurther performed for 2.5 hours).

Furthermore, charging was performed at a current of 0.2 C to an SOC of50%, and then constant-current discharging was performed in alow-temperature environment at −30° C. for 2 seconds at varying currentsof ⅛ C, ¼ C, ½ C, 1.5 C, and 2 C. The battery voltage drop at 2 secondsafter discharging under each condition was measured. From eachmeasurement, a current I that could be passed in 2 seconds when theupper limit charge voltage was 3 V was calculated, and a valuecalculated from the formula: 3×I (W) was defined as the low-temperatureoutput characteristics of each battery.

TABLE 2B Low-Temperature Output Characteristics, Discharge (ComparativeCapacity, Example B4 = mAh/g 100) Example B16 367 131 Comparative 365100 Example B4

The carbon material produced in Example B16 had a discharge capacity andlow-temperature output characteristics sufficiently superior to those ofthe carbon material produced in Comparative Example B4.

A carbonaceous material having lower crystallinity than the raw carbonmaterial was deposited on the carbon material obtained by the presentinvention to produce a carbon material, and batteries produced usingthis carbon material were evaluated. The production of this carbonmaterial (Examples B24 and B25) and Comparative Example B5 will bedescribed below, and the evaluation results of the batteries are shownin Table 3B.

Example B24

A flake natural graphite having a d50 of 100 μm was crushed with a dryswirl-flow crusher to give a flake natural graphite having a d50 of 8.1μm, a Tap of 0.39 g/cm³, and a water content of 0.08% by mass. To 100 gof the resulting flake natural graphite, 12 g of a granulating agent ofa liquid paraffin (Wako Pure Chemical Industries, Ltd., first grade,physical properties at 25° C.: viscosity=95 cP, contact angle=13.2°,surface tension=31.7 mN/m, r cos θ=30.9) was added and mixed withstirring. The sample obtained was disintegrated and mixed using a hammermill (MF10 available from IKA) at a rotation speed of 3,000 rpm to givea flake natural graphite to which the granulating agent uniformlyadhered. Using a Model NHS-1 hybridization system available from NaraMachinery Co., Ltd., the sample obtained was mechanically spheroidizedat a rotor peripheral speed of 85 m/sec for 10 minutes to givegranulated carbon material particles.

The granulated carbon material particles and a coal-tar pitch, servingas a carbonaceous material precursor having lower crystallinity than theraw carbon material, were mixed using a mixer at 120° C. for 20 minutes.The resulting mixture was heat treated in an inert gas at 1,300° C. for1 hour, and then the burned product was disintegrated and classified togive multi-layered graphite particles made of the granulated carbonmaterial particles and the carbonaceous material having lowercrystallinity than the raw carbon material combined with each other. Theburning yield showed that the mass ratio of the granulated carbonmaterial particles to the carbonaceous material having lowercrystallinity than the raw carbon material (granulated carbon materialparticle/amorphous carbon) of the multi-layered graphite particles was1:0.065. The d50, SA, Tap, discharge capacity, and low-temperatureoutput characteristics of the sample obtained were measured. The resultsare shown in Table 3B.

Example B25

Multi-layered graphite particles were obtained in the same manner as inExample B24 except that the mass ratio of the granulated carbon materialparticles to the carbonaceous material having lower crystallinity thanthe raw carbon material (granulated carbon material particle/amorphouscarbon) of the multi-layered graphite particles was 1:0.08. The resultsof the measurements made in the same manner as in Example B24 are shownin Table 3B.

Comparative Example B5

A multi-layered carbon material was obtained in the same manner as inExample B24 except that the granulated carbon material particles werereplaced with the sample obtained in Comparative Example B4. The resultsof the measurements made in the same manner as in Example B24 are shownin Table 3B.

TABLE 3B Low-Temperature Output Characteristics, Discharge (Comparatived50, Tap SA, Capacity, Example B5 = μm g/cm³ m²/g mAh/g 100) Example B2412.0 1.05 7.9 362 139 Example B25 11.8 1.02 7.1 359 147 Comparative 11.41.04 3.1 362 100 Example B5

In Examples B24 and B25, the low-temperature output characteristics wassufficiently superior to those of Comparative Example B5.

Third examples (Examples C) of the present invention will now bedescribed.

The properties of the carbon materials of Examples C or ComparativeExamples C were measured as described below.

Measurement of Volume-Based Median Diameter d50

A sample in an amount of 0.01 g was suspended in 10 mL of ethanol. Thesuspension was placed in a laser diffraction/scattering particle sizedistribution analyzer (LA-920 available from HORIBA, Ltd.) andirradiated with ultrasonic waves of 28 kHz at a power of 60 W for 1minute, and then a volume-based median diameter d50 was measured(ultrasonic intensity, 4; relative refractive index, 1.50). In ExamplesC3 and C4 and Comparative Examples C3 and C4, 10 mL of a 0.2% by volumeaqueous solution of polyoxyethylene sorbitan monolaurate (registeredtrademark, Tween 20) was used as a dispersion medium in place ofethanol.

Frequency of Particles with Diameter of 5 μm or Less

A sample in an amount of 0.2 g was suspended in 50 mL of ethanol. Thesuspension was placed in a flow-type particle image analyzer (FPIA-2000available from Sysmex Industrial Corp.) and irradiated with ultrasonicwaves of 28 kHz at a power of 60 W for a predetermined time, and thenthe number of particles was counted with a detection range set to 0.6 to400 μm to determine the percentage of the number of particles with adiameter of 5 μm or less in the total. In Examples C3 and C4 andComparative Examples C3 and C4, 50 mL of a 0.2% by volume aqueoussolution of polyoxyethylene sorbitan monolaurate (registered trademark,Tween 20) was used as a dispersion medium in place of ethanol.

Tap Density

The tap density was measured using a powder density meter (Tap Denseravailable from Hosokawa Micron Corporation) as follows: a sample wasdropped through a sieve with openings of 300 μm into a cylindrical tapcell with a diameter of 1.6 cm and a volume capacity of 20 cm³ to fillup the cell; a tap with a stroke length of 10 mm was given 1,000 times;the volume at this time was measured; and the density was calculatedfrom the volume and the mass of the sample.

Roundness

A sample in an amount of 0.2 g was suspended in 50 mL of a 0.2% by massaqueous solution of polyoxyethylene sorbitan monolaurate (registeredtrademark, Tween 20). The suspension was placed in a flow-type particleimage analyzer (FPIA available from Sysmex Industrial Corp.) andirradiated with ultrasonic waves of 28 kHz at a power of 60 W for 1minute, and then the roundness of particles with a diameter in the rangeof 1.5 to 40 μm was measured with a detection range set to 0.6 to 400μm. The ratio of the perimeter of a circle (equivalent circle) havingthe same area as the projected particle shape measured, as thenumerator, to the perimeter of the projected particle shape measured, asthe denominator, was calculated, and the average was calculated todetermine the roundness.

BET Specific Surface Area

Using a surface area meter (Gemini 2360 specific surface area analyzeravailable from Shimadzu Corporation), a sample was preliminarily vacuumdried under a nitrogen stream at 100° C. for 3 hours and then cooled toliquid nitrogen temperature, and using a nitrogen-helium mixed gasprecisely regulated so as to have a nitrogen pressure of 0.3 relative toatmospheric pressure, a BET specific surface area was measured by anitrogen adsorption BET multipoint method according to a flowing gasmethod.

Lc and d₀₀₂

X-ray standard high-purity silicon powder was added to a sample toprepare a mixture containing 15% by mass of the sample. Using a CuKαradiation monochromatized with a graphite monochromator as a radiationsource, a wide-angle X-ray diffractometry curve was obtained byreflection diffractometry. The method of the Japan Society for Promotionof Scientific Research was used to determine an interplanar spacing(d₀₀₂) and a crystallite size (Lc).

Amounts of Eliminated CO and CO₂ During Temperature Rise from RoomTemperature to 1,000° C. Using Pyrolysis Mass Spectrometer (TPD-MS)

A sample was heat treated under a nitrogen stream at 200° C. for 5hours. After that, the temperature was raised from room temperature to1,000° C. at a rate of 10° C./min under a stream of He gas at 50 mL/min.The amounts of CO and CO₂ generated during this process werequantitatively measured using a pyrolysis mass spectrometer (TPD-MS) tomeasure the amount of eliminated CO (μmol/g) and the amount ofeliminated CO₂ (μmol/g) per gram of the sample.

The production of electrode sheets and non-aqueous batteries (laminatebatteries) each including the carbon material of Examples or ComparativeExamples was carried out as described below.

Preparation of Electrode Sheet

An electrode plate having an active material layer with an activematerial layer density of 1.60±0.03 g/cm³ was prepared using a carbonmaterial of Examples or Comparative Examples. Specifically, 50.00±0.02 gof a carbon material, 50.00±0.02 g (0.500 g on a solids basis) of a 1%by mass carboxymethylcellulose sodium salt aqueous solution, and1.00±0.05 g (0.5 g on a solids basis) of an aqueous dispersion of astyrene-butadiene rubber having a weight average molecular weight of270,000 were stirred with a Keyence hybrid mixer for 5 minutes, and themixture was defoamed for 30 seconds to give a slurry.

The slurry was applied to a 10-μm-thick copper foil, serving as acurrent collector, to a width of 10 cm using a small die coateravailable from Itochu Machining Co., Ltd. such that the carbon materialadhered in an amount of 12.00±0.3 mg/cm². The coated foil wasroll-pressed using a roller having a diameter of 20 cm to adjust thedensity of the active material layer to be 1.60±0.03 g/cm³, therebypreparing an electrode sheet.

Method of Producing Non-Aqueous Secondary Battery (Laminate Battery)

The electrode sheet was cut to 4 cm×3 cm to prepare a negativeelectrode, and a positive electrode made of LiNi_(1/3)Mn_(1/3)CO_(1/3)O₂(NMC) was cut to the same area. The negative electrode and the positiveelectrode were combined with a separator (made of a porous polyethylenefilm) placed therebetween. An electrolyte solution of 1.2 mol/L of LiPF₆in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, anddimethyl carbonate (volume ratio=3:3:4) was injected in an amount of 250μL to produce a laminate battery.

The characteristics of the laminate batteries produced were measured asdescribed below.

Initial Low-Temperature Output Characteristics

The initial low-temperature output characteristics of the laminatebatteries were measured by the following method.

A laminate battery that had yet to go through a charge and dischargecycle was subjected to an initial charge and discharge that involvesthree cycles in a voltage range of 4.1 V to 3.0 V at 25° C. and acurrent of 0.2 C (1 C is a current at which a rated capacity at a 1-hourrate discharge capacity is discharged in 1 hour, and so on) and twocycles in a voltage range of 4.2 V to 3.0 V at a current of 0.2 C (incharging, a constant-voltage charge at 4.2 V was further performed for2.5 hours).

For the battery that had been subjected to the initial charge anddischarge, charging was further performed at a current of 0.2 C to acharging rate (SOC, State Of Charge) of 50%, and then constant-currentdischarging was performed in a low-temperature environment at −30° C.for 2 seconds at varying currents of ⅛ C, ¼ C, ½ C, 1.5 C, and 2 C. Thebattery voltage drop at 2 seconds after discharging under each conditionwas measured. From each measurement, a current I that could be passed in2 seconds when the upper limit charge voltage was 3 V was calculated,and a value calculated from the formula: 3×I (W) was defined as thelow-temperature output characteristics in initial 2 seconds of eachbattery.

Likewise, a current I that could be passed in 10 seconds was calculated,and the calculated value was defined as the low-temperature outputcharacteristics in initial 10 seconds.

Post-Cycle Low-Temperature Output Characteristics

The post-cycle low-temperature output characteristics of the laminatebatteries were measured by the following method.

A laminate battery that had yet to go through a charge and dischargecycle was subjected to a charge and discharge that involves 3 cycles ina voltage range of 4.1 V to 3.0 V at 25° C. and a current of 0.2 C and300 cycles in a voltage range of 4.2 V to 3.0 V at a current of 0.2 C(in charging, a constant-voltage charge at 4.2 V was further performedfor 2.5 hours).

For the battery that had been subjected to the 300-cycle charge anddischarge, charging was performed at a current of 0.2 C to a chargingrate (SOC) of 50%, and then constant-current discharging was performedin a low-temperature environment at −30° C. for 2 seconds at varyingcurrents of ⅛ C, ¼ C, ½ C, 1.5 C, and 2 C. The battery voltage drop at 2seconds after discharging under each condition was measured. From eachmeasurement, a current I that could be passed in 2 seconds when theupper limit charge voltage was 3 V was calculated, and a valuecalculated from the formula: 3×I (W) was defined as the low-temperatureoutput characteristics in post-cycle 2 seconds of each battery.

Likewise, a current I that could be passed in 10 seconds was calculated,and the calculated value was defined as the low-temperature outputcharacteristics in post-cycle 10 seconds.

Production of Non-Aqueous Secondary Battery (2016 Coin Battery)

The electrode sheet prepared by the above-described method was cut intoa disk having a diameter of 12.5 mm, and lithium metal foil was cut intoa disk having a diameter of 14 mm to prepare a counter electrode. Aseparator (made of a porous polyethylene film) was placed between thetwo electrodes, the separator being impregnated with an electrolytesolution of 1 mol/L of LiPF₆ in a mixed solvent of ethylene carbonateand ethyl methyl carbonate (volume ratio=3:7). In this manner, 2016 coinbatteries were produced.

Method for Measuring Initial Discharge Capacity

Using the non-aqueous secondary battery (2016 coin battery) produced bythe above-described method, the capacity of the battery during chargingand discharging was measured by the following method.

The lithium counter electrode was charged to 5 mV at a current densityof 0.05 C and further charged at a constant voltage of 5 mV to a currentdensity of 0.005 C. The negative electrode was doped with lithium, andthen the lithium counter electrode was discharged to 1.5 V at a currentdensity of 0.1 C. Subsequently, a second charging and discharging wasperformed at the same current density. The discharge capacity at thesecond cycle was defined as an initial discharge capacity (1st dischargecapacity) of this battery.

Example C1

A flake natural graphite having a volume-based median diameter d50 of100 μm was crushed with a mechanical crusher (Turbo Mill available fromFreund Corporation) having a crushing rotor and a liner to give a flakenatural graphite having a volume-based median diameter d50 of 30 μm.Using an NHS-1 hybridization system available from Nara Machinery Co.,Ltd., 300 g of the flake natural graphite was mechanically spheroidizedat a rotor peripheral speed of 88 m/sec for 1 minute while fine powdergenerated during the spheroidization was deposited on the base materialand incorporated into the spheroidized particles. The spheroidizedgraphite was further spheroidized for 2 minutes while 30 g of a liquidparaffin (Wako Pure Chemical Industries, Ltd., first grade; flash point,238° C.) was added to the spheroidized graphite to reduce the amount ofexposure of the graphite to oxygen. The gas phase during the process wassampled and analyzed by gas chromatography to show that the amount of COand the amount of CO₂ generated from 1 kg of the flake natural graphitewere respectively 0.3 mmol and 0.9 mmol.

The carbon material obtained had a D50 (μm), a volume-based mediandiameter, of 15.0 μm, a Q_(5min) (%), a frequency of particles with adiameter of 5 μm or less (fine powder content) after ultrasonicirradiation for 5 minutes, of 13%, and a Q_(5min) (%)/D50 (μm) of 0.9.

The carbon material had a Q_(1min) (%), a frequency of particles with adiameter of 5 μm or less (fine powder content) after ultrasonicirradiation for 1 minute, of 5%, a Q_(10min) (%), a frequency ofparticles with a diameter of 5 μm or less (fine powder content) afterultrasonic irradiation for 10 minutes, of 27%, a Q_(1min) (%)/D50 (μm)of 0.3, and a Q_(10min) (%)/D50 (μm) of 1.8.

The carbon material had a roundness of 0.89, a tap density of 0.79g/cm³, and a BET specific surface area of 12.9 m²/g.

The carbon material was embedded in a resin to prepare a sample forcross-sectional observation, and a cross section was observed under ascanning electron microscope to show that the carbon material was formedof different graphite particles.

The amount of eliminated CO and the amount of CO₂ of the carbon materialduring the temperature rise from room temperature to 1,000° C. using apyrolysis mass spectrometer (TPD-MS) were respectively 9 μmol/g and 2μmol/g.

The carbon material had an Lc, as determined by wide-angle X-raydiffractometry, of 100 nm or more and a d₀₀₂ of 0.336 nm.

The physical properties of the carbon material are shown in Tables 1C to3C. Initial output characteristics and post-cycle output characteristicsof laminate batteries produced using the carbon material and initialdischarge capacities of coin batteries produced using the carbonmaterial are shown in Table 4C.

Example C2

The same procedure as in Example C1 was repeated except that a flakenatural graphite and a liquid paraffin were mixed before spheroidizationand then spheroidized for 3 minutes so that the amount of CO and theamount of CO₂ generated from 1 kg of the flake natural graphite would berespectively 0.3 mmol and 1.0 mmol.

The carbon material obtained had a Q_(5min) (%)/D50 (μm) of 1.1.

The carbon material was embedded in a resin to prepare a sample forcross-sectional observation, and a cross section was observed under ascanning electron microscope to show that the carbon material was formedof different graphite particles. The physical properties of the carbonmaterial are shown in Tables 1C to 3C. The properties of laminatebatteries and coin batteries produced using the carbon material areshown in Table 4C.

Example C3

The same procedure as in Example C1 was repeated except that thespheroidization was carried out using ethylene glycol (Wako PureChemical Industries, Ltd., first grade; flash point, 110° C.) in placeof the liquid paraffin so that the amount of CO and the amount of CO₂generated from 1 kg of the flake natural graphite would be respectively2.1 mmol and 4.0 mmol. Furthermore, the carbon material obtained wasdried in a nitrogen atmosphere at 250° C.

The carbon material obtained had a Q_(5min) (%)/D50 (μm) of 1.9.

The carbon material was embedded in a resin to prepare a sample forcross-sectional observation, and a cross section was observed under ascanning electron microscope to show that the carbon material was formedof different graphite particles.

The physical properties of the carbon material are shown in Tables 1C to3C. The properties of laminate batteries and coin batteries producedusing the carbon material are shown in Table 4C.

Example C4

The same procedure as in Example C3 was repeated except that a flakegraphite and ethylene glycol were mixed before spheroidization andspheroidized for 3 minutes in an apparatus for applying a mechanicalaction(s) so that the amount of CO and the amount of CO₂ generated from1 kg of the flake natural graphite would be respectively 2.5 mmol and5.0 mmol.

The carbon material obtained had a Q_(5min) (%)/D50 (μm) of 2.3.

The carbon material was embedded in a resin to prepare a sample forcross-sectional observation, and a cross section was observed under ascanning electron microscope to show that the carbon material was formedof different graphite particles.

The physical properties of the carbon material are shown in Tables 1C to3C. The properties of laminate batteries and coin batteries producedusing the carbon material are shown in Table 4C.

Comparative Example C1

The same procedure as in Example C1 was repeated except that the flakenatural graphite having a volume-based median diameter d50 of 30 μm usedin Example C1 was spheroidized in an air atmosphere. The gas phaseduring the process was sampled and analyzed by gas chromatography toshow that the amount of CO and the amount of CO₂ generated from 1 kg ofthe flake natural graphite were respectively 7.2 mmol and 11.2 mmol.

The carbon material obtained had a D50 (μm), a volume-based mediandiameter, of 14.4 μm, a Q_(5min) (%), a frequency of particles with adiameter of 5 μm or less (fine powder content) after 5-minuteultrasonic, of 75%, and a Q_(5min) (%)/D50 (μm) of 5.2.

The carbon material was embedded in a resin to prepare a sample forcross-sectional observation, and a cross section was observed under ascanning electron microscope to show that the carbon material was formedof different graphite particles.

The physical properties of the carbon material are shown in Tables 1C to3C. The properties of laminate batteries and coin batteries producedusing the carbon material are shown in Table 4C.

Comparative Example C2

The carbon material of Comparative Example C1 obtained through thespheroidization was dried in a nitrogen atmosphere in the same manner asin Example C3 to prepare a carbon material of Comparative Example C2.

The carbon material obtained had a Q_(5min) (%)/D50 (μm) of 5.3.

The carbon material was embedded in a resin to prepare a sample forcross-sectional observation, and a cross section was observed under ascanning electron microscope to show that the carbon material was formedof different graphite particles.

The physical properties of the carbon material are shown in Tables 1C to3C. The properties of laminate batteries and coin batteries producedusing the carbon material are shown in Table 4C.

Comparative Example C3

A commercially available spheroidized natural graphite A had a D50 (μm)of 20.3 μm, a Q_(5min) (%) of 76%, and a Q_(5min) (%)/D50 (μm) of 3.7,as measured in the same manner as in Example C3.

The natural graphite A was embedded in a resin to prepare a sample forcross-sectional observation, and a cross section was observed under ascanning electron microscope to show that natural graphite A was formedof different graphite particles.

The physical properties of the natural graphite A are shown in Tables 1Cand 3C. The properties of laminate batteries and coin batteries producedusing the natural graphite A are shown in Table 4C.

Comparative Example C4

A commercially available spheroidized natural graphite B had a D50 (μm)of 16.0 μm, a Q_(5min) (%) of 69%, and a Q_(5min) (%)/D50 (μm) of 4.3,as measured in the same manner as in Comparative Example C3.

The natural graphite B was embedded in a resin to prepare a sample forcross-sectional observation, and a cross section was observed under ascanning electron microscope to show that natural graphite B was formedof different graphite particles.

The physical properties of the natural graphite B are shown in Tables 1Cand 3C. The properties of laminate batteries and coin batteries producedusing the natural graphite B are shown in Table 4C.

TABLE 1C Q_(5 min) Q_(1 min) Q_(10 min) (%)/D50 (%)/D50 (%)/D50Q_(5 min) Q_(1 min) Q_(10 min) (μm) 0 (μm) (μm) (%) (%) (%) Example C10.9 0.3 1.8 13 5 27 Example C2 1.1 0.5 1.8 16 7 26 Example C3 1.9 0.62.9 28 9 42 Example C4 2.3 0.6 2.8 33 9 40 Comparative 5.2 5.0 5.3 75 7277 Example C1 Comparative 5.3 5.1 5.4 76 73 78 Example C2 Comparative3.7 2.7 4.1 76 55 83 Example C3 Comparative 4.3 3.0 4.8 69 48 76 ExampleC4

TABLE 2C Amount of Amount of Amount of eliminated CO + eliminated COeliminated CO₂ CO₂ (μmol/g) (μmol/g) (μmol/g) during during duringtemperature temperature temperature rise from room rise from room risefrom room temperature to temperature to temperature to 1,000° C., as1,000° C., as 1,000° C., as determined by determined by determined byTPD-MS TPD-MS TPD-MS Example C1 11 9 2 Example C2  11* 10 2 Example C351 40 11 Example C4 62 49 13 Comparative 163  130 33 Example C1Comparative 155  127 28 Example C2 Comparative — — — Example C3Comparative — — — Example C4 *11 (μmol/g) is a value obtained byrounding off 11.3 (μmol/g), the total amount of the amount of eliminatedCO 9.7 (μmol/g) and the amount of eliminated CO₂ 1.6 (μmol/g), to thenearest integer.

TABLE 3C BET Volume- Specific Based Tap Surface Median Density AreaDiameter Lc d₀₀₂ (g/cm³) Roundness (m²/g) (μm) (nm) (nm) Example C1 0.790.89 12.9 15.0 >100 0.336 Example C2 0.85 0.89 13.5 14.7 >100 0.336Example C3 0.98 0.90 11.7 14.7 >100 0.336 Example C4 0.98 0.90 11.714.5 >100 0.336 Comparative 0.76 0.87 11.0 14.4 >100 0.336 Example C1Comparative 0.73 0.88 11.0 14.4 >100 0.336 Example C2 Comparative 0.920.89 5.1 20.3 >100 0.336 Example C3 Comparative 1.02 0.93 7.0 16.0 >1000.336 Example C4

TABLE 4C Low- Low- Low- Low-Tem- Tem- Tem- Tem- perature peratureperature perature Output in Output in Output in Output in Post-CycleInitial Initial 2 Initial 10 Post-Cycle 10 Discharge Seconds Seconds 2Seconds Seconds Capacity (W) (W) (W) (W) (mAh/g) Example C1 0.093 0.0760.068 0.044 365 Example C2 0.098 0.080 0.068 0.043 365 Example C3 0.0790.064 0.060 0.040 364 Example C4 0.083 0.068 0.062 0.041 362 Comparative0.074 0.061 0.055 0.038 365 Example C1 Comparative 0.077 0.063 0.0550.038 365 Example C2 Comparative 0.046 0.037 0.044 0.027 368 Example C3Comparative 0.060 0.047 0.049 0.030 368 Example C4

The batteries produced using Examples C1 to C4, the carbon materials ofthe present invention, have high and excellent initial and post-cyclelow-temperature output characteristics. By contrast, the carbonmaterials used in Comparative Examples C1 to C4 have a Q_(5min) (%) toD50 (μm) ratio outside the prescribed range, where Q_(5min) is afrequency of particles with a diameter of 5 μm or less (fine powdercontent) after ultrasonic irradiation for 5 minutes, and D50 is avolume-based median diameter, and thus provide low initial andpost-cycle low-temperature output characteristics.

Fourth examples (Examples D) of the present invention will now bedescribed.

Preparation of Electrode Sheet

An electrode plate having an active material layer with an activematerial layer density of 1.50±0.03 g/cm³ was prepared using graphiteparticles of Examples or Comparative Examples. Specifically, 50.00±0.02g of a negative electrode material (carbon material), 50.00±0.02 g(0.500 g on a solids basis) of a 1% by mass aqueouscarboxymethylcellulose sodium salt solution, and 1.00±0.05 g (0.5 g on asolids basis) of an aqueous dispersion of a styrene-butadiene rubberhaving a weight average molecular weight of 270,000 were stirred with aKeyence hybrid mixer for 5 minutes, and the mixture was defoamed for 30seconds to give a slurry.

The slurry was applied to a 10-μm-thick copper foil, serving as acurrent collector, to a width of 10 cm using a small die coateravailable from Itochu Machining Co., Ltd. such that the negativeelectrode material adhered in an amount of 6.00±0.3 mg/cm² or 12.00±0.3mg/cm². The coated foil was roll-pressed using a roller having adiameter of 20 cm to adjust the density of the active material layer tobe 1.50±0.03 g/cm³, thereby preparing an electrode sheet.

Production of Non-Aqueous Secondary Battery (2016 Coin Battery)

The electrode sheet prepared by the above-described method, to which thenegative electrode material adhered in an amount of 12.00±0.3 mg/cm²,was cut into a disk having a diameter of 12.5 mm, and lithium metal foilwas cut into a disk having a diameter of 14 mm to prepare a counterelectrode. A separator (made of a porous polyethylene film) was placedbetween the two electrodes, the separator being impregnated with anelectrolyte solution of 1 mol/L of LiPF₆ in a mixed solvent of ethylenecarbonate and ethyl methyl carbonate (volume ratio=3:7). In this manner,2016 coin batteries were produced.

Method of Producing Non-Aqueous Secondary Battery (Laminate Battery)

The electrode sheet prepared by the above-described method, to which thenegative electrode material adhered in an amount of 6.00±0.3 mg/cm², wascut to 4 cm×3 cm to prepare a negative electrode, and a positiveelectrode made of NMC was cut to the same area. The negative electrodeand the positive electrode were combined with a separator (made of aporous polyethylene film) placed therebetween. An electrolyte solutionof 1.2 mol/L of LiPF₆ in a mixed solvent of ethylene carbonate, ethylmethyl carbonate, and dimethyl carbonate (volume ratio=3:3:4) wasinjected in an amount of 250 μL to produce a laminate battery.

Method for Measuring 1st Discharge Capacity

Using the non-aqueous secondary battery (2016 coin battery) produced bythe above-described method, the capacity of the battery during chargingand discharging was measured by the following method.

The lithium counter electrode was charged to 5 mV at a current densityof 0.04 C and further charged at a constant voltage of 5 mV to a currentdensity of 0.005 C. The negative electrode was doped with lithium, andthen the lithium counter electrode was discharged to 1.5 V at a currentdensity of 0.08 C. Subsequently, a second charging and discharging wasperformed at the same current density. The discharge capacity at thesecond cycle was defined as a 1st discharge capacity of this battery.

Low-Temperature Output Characteristics

Using the laminate non-aqueous electrolyte secondary battery produced bythe method for producing a non-aqueous electrolyte secondary batterydescribed above, low-temperature output characteristics were measured bythe following method.

A non-aqueous electrolyte secondary battery that had yet to go through acharge and discharge cycle was subjected to an initial charge anddischarge that involves three cycles in a voltage range of 4.1 V to 3.0V at 25° C. and a current of 0.2 C (1 C is a current at which a ratedcapacity at a 1-hour rate discharge capacity is discharged in 1 hour,and so on) and two cycles in a voltage range of 4.2 V to 3.0 V at acurrent of 0.2 C (in charging, a constant-voltage charge at 4.2 V wasfurther performed for 2.5 hours).

Furthermore, charging was performed at a current of 0.2 C to an SOC of50%, and then constant-current discharging was performed in alow-temperature environment at −30° C. for 2 seconds at varying currentsof ⅛ C, ¼ C, ½ C, 1.5 C, and 2 C. The battery voltage drop at 2 secondsafter discharging under each condition was measured. From eachmeasurement, a current I that could be passed in 2 seconds when theupper limit charge voltage was 3 V was calculated, and a valuecalculated from the formula: 3×I (W) was defined as the low-temperatureoutput characteristics of each battery.

Average Particle Diameter d50; d50

The d50 was determined as a volume-based median diameter by suspending0.01 g of a carbon material in 10 mL of a 0.2% by mass aqueous solutionof a polyoxyethylene sorbitan monolaurate surfactant (Tween 20(registered trademark)), placing the suspension (a measurement sample)in a commercially available laser diffraction/scattering particle sizedistribution analyzer (e.g., LA-920 available from HORIBA, Ltd.),irradiating the measurement sample with ultrasonic waves of 28 kHz at apower of 60 W for 1 minute, and then performing a measurement with theanalyzer.

Tap Density; Tap (Y_(d))

Using a powder density meter, the carbon material of the presentinvention was dropped through a sieve with openings of 300 μm into acylindrical tap cell with a diameter of 1.6 cm and a volume capacity of20 cm³ to fill up the cell, and then a tap with a stroke length of 10 mmwas given 1,000 times. The density calculated from the volume at thistime and the mass of the sample was defined as the tap density.

Specific Surface Area Determined by BET Method; SA (X_(d))

Using a surface area meter (fully automatic surface area analyzeravailable from Ohkura Riken Co., Ltd.), a carbon material sample waspreliminarily dried under a nitrogen stream at 350° C. for 15 minutes,and then using a nitrogen-helium mixed gas precisely regulated so as tohave a nitrogen pressure of 0.3 relative to atmospheric pressure, a BETspecific surface area was measured by a nitrogen adsorption BETmultipoint method according to a flowing gas method.

Example D1

A flake natural graphite having a d50 of 100 μm was crushed with amechanical crusher having a crushing rotor and a liner to give a flakenatural graphite having a d50 of 30 μm and a water content of 0.03% bymass. To 100 g of the resulting flake natural graphite, 6 g of agranulating agent of a paraffinic oil (liquid paraffin available fromWako Pure Chemical Industries, Ltd., first grade, physical properties at25° C.: viscosity=95 cP, contact angle=13.2°, surface tension=31.7 mN/m,r cos θ=30.9) was added and mixed with stirring. The sample obtained wasdisintegrated and mixed using a hammer mill (MF10 available from IKA) ata rotation speed of 3,000 rpm to give a flake natural graphite to whichthe granulating agent uniformly adhered. Using a Model NHS-1hybridization system available from Nara Machinery Co., Ltd., the flakenatural graphite to which the granulating agent uniformly adhered wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes while fine powder generated during the spheroidization wasdeposited on the base material and incorporated into the spheroidizedparticles, thereby providing a spheroidized natural graphite having ad50 of 19.4 μm. The spheroidized natural graphite and a coal-tar pitch,serving as an amorphous carbon precursor, were mixed and heat treated inan inert gas at 1,300° C., and then the burned product was disintegratedand classified to give a multi-layered carbon material made of graphiteparticles and an amorphous carbon combined with each other. The burningyield showed that the mass ratio of spheroidized graphite particle toamorphous carbon (spheroidized graphite particle/amorphous carbon) ofthe multi-layered carbon material was 1:0.030. Using the measurementmethods described above, d50, SA, Tap, 1st discharge capacity, andlow-temperature output characteristics were measured. The results areshown in Table 1D.

Example D2

The spheroidized natural graphite obtained in Example D1 and a coal-tarpitch, serving as an amorphous carbon precursor, were mixed and heattreated in an inert gas at 1,300° C., and then the burned product wasdisintegrated and classified to give a multi-layered carbon materialmade of graphite particles and an amorphous carbon combined with eachother. The burning yield showed that the mass ratio of spheroidizedgraphite particle to amorphous carbon (spheroidized graphiteparticle/amorphous carbon) of the multi-layered carbon material was1:0.042. The results of the measurements made in the same manner as inExample D1 are shown in Table 1D.

Example D3

The spheroidized natural graphite obtained in Example D1 and a coal-tarpitch, serving as an amorphous carbon precursor, were mixed and heattreated in an inert gas at 1,300° C., and then the burned product wasdisintegrated and classified to give a multi-layered carbon materialmade of graphite particles and an amorphous carbon combined with eachother. The burning yield showed that the mass ratio of spheroidizedgraphite particle to amorphous carbon (spheroidized graphiteparticle/amorphous carbon) of the multi-layered carbon material was1:0.050. The results of the measurements made in the same manner as inExample D1 are shown in Table 1D.

Example D4

The spheroidized natural graphite obtained in Example D1 and a coal-tarpitch, serving as an amorphous carbon precursor, were mixed and heattreated in an inert gas at 1,300° C., and then the burned product wasdisintegrated and classified to give a multi-layered carbon materialmade of graphite particles and an amorphous carbon combined with eachother. The burning yield showed that the mass ratio of spheroidizedgraphite particle to amorphous carbon (spheroidized graphiteparticle/amorphous carbon) of the multi-layered carbon material was1:0.065. The results of the measurements made in the same manner as inExample D1 are shown in Table 1D.

Example D5

The spheroidized natural graphite obtained in Example D1 and a coal-tarpitch, serving as an amorphous carbon precursor, were mixed and heattreated in an inert gas at 1,300° C., and then the burned product wasdisintegrated and classified to give a multi-layered carbon materialmade of graphite particles and an amorphous carbon combined with eachother. The burning yield showed that the mass ratio of spheroidizedgraphite particle to amorphous carbon (spheroidized graphiteparticle/amorphous carbon) of the multi-layered carbon material was1:0.100. The results of the measurements made in the same manner as inExample D1 are shown in Table 1D.

Comparative Example D1

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite and flake graphite fine powder generated duringthe spheroidization that were not deposited on the base material orincorporated. This sample was classified to remove the flake graphitefine powder, thereby providing a spheroidized graphite having a d50 of10.8 μm.

The spheroidized natural graphite and a coal-tar pitch, serving as anamorphous carbon precursor, were mixed and heat treated in an inert gasat 1,300° C., and then the burned product was disintegrated andclassified to give a multi-layered carbon material made of graphiteparticles and an amorphous carbon combined with each other. The burningyield showed that the mass ratio of spheroidized graphite particle toamorphous carbon (spheroidized graphite particle/amorphous carbon) ofthe multi-layered carbon material was 1:0.020. The results of themeasurements made in the same manner as in Example D1 are shown in Table1D.

Comparative Example D2

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite and flake graphite fine powder generated duringthe spheroidization that were not deposited on the base material orincorporated. This sample was classified to remove the flake graphitefine powder, thereby providing a spheroidized graphite having a d50 of10.8 μm. The spheroidized natural graphite and a coal-tar pitch, servingas an amorphous carbon precursor, were mixed and heat treated in aninert gas at 1,300° C., and then the burned product was disintegratedand classified to give a multi-layered carbon material made of graphiteparticles and an amorphous carbon combined with each other. The burningyield showed that the mass ratio of spheroidized graphite particle toamorphous carbon (spheroidized graphite particle/amorphous carbon) ofthe multi-layered carbon material was 1:0.040. The results of themeasurements made in the same manner as in Example D1 are shown in Table1D.

Comparative Example D3

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 3minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite and flake graphite fine powder generated duringthe spheroidization that were not deposited on the base material orincorporated. This sample was classified to remove the flake graphitefine powder, thereby providing a spheroidized graphite having a d50 of15.7 μm. The spheroidized natural graphite and a coal-tar pitch, servingas an amorphous carbon precursor, were mixed and heat treated in aninert gas at 1,300° C., and then the burned product was disintegratedand classified to give a multi-layered carbon material made of graphiteparticles and an amorphous carbon combined with each other. The burningyield showed that the mass ratio of spheroidized graphite particle toamorphous carbon (spheroidized graphite particle/amorphous carbon) ofthe multi-layered carbon material was 1:0.015. The results of themeasurements made in the same manner as in Example D1 are shown in Table1D.

Comparative Example D4

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 3minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite and flake graphite fine powder generated duringthe spheroidization that were not deposited on the base material orincorporated. This sample was classified to remove the flake graphitefine powder, thereby providing a spheroidized graphite having a d50 of15.7 μm. The spheroidized natural graphite and a coal-tar pitch, servingas an amorphous carbon precursor, were mixed and heat treated in aninert gas at 1,300° C., and then the burned product was disintegratedand classified to give a multi-layered carbon material made of graphiteparticles and an amorphous carbon combined with each other. The burningyield showed that the mass ratio of spheroidized graphite particle toamorphous carbon (spheroidized graphite particle/amorphous carbon) ofthe multi-layered carbon material was 1:0.040. The results of themeasurements made in the same manner as in Example D1 are shown in Table1D.

Comparative Example D5

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite and flake graphite fine powder generated duringthe spheroidization that were not deposited on the base material orincorporated. This sample was classified to remove the flake graphitefine powder, thereby providing a spheroidized graphite having a d50 of10.8 μm. The spheroidized natural graphite and a coal-tar pitch, servingas an amorphous carbon precursor, were mixed and heat treated in aninert gas at 1,300° C., and then the burned product was disintegratedand classified to give a multi-layered carbon material made of graphiteparticles and an amorphous carbon combined with each other. The burningyield showed that the mass ratio of spheroidized graphite particle toamorphous carbon (spheroidized graphite particle/amorphous carbon) ofthe multi-layered carbon material was 1:0.013. The results of themeasurements made in the same manner as in Example D1 are shown in Table1D.

Comparative Example D6

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 3minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite and flake graphite fine powder generated duringthe spheroidization that were not deposited on the base material orincorporated. This sample was classified to remove the flake graphitefine powder, thereby providing a spheroidized graphite having a d50 of19.5 μm. The spheroidized natural graphite and a coal-tar pitch, servingas an amorphous carbon precursor, were mixed and heat treated in aninert gas at 1,300° C., and then the burned product was disintegratedand classified to give a multi-layered carbon material made of graphiteparticles and an amorphous carbon combined with each other. The burningyield showed that the mass ratio of spheroidized graphite particle toamorphous carbon (spheroidized graphite particle/amorphous carbon) ofthe multi-layered carbon material was 1:0.075. The results of themeasurements made in the same manner as in Example D1 are shown in Table1D.

TABLE 1D 1st Low- Dis- Temper- Tap charge ature d50 SA (X_(d)) (Y_(d))10Y_(d) + Capacity Output (μm) (m²/g) (g/cm³) 0.26X_(d) (mAh/g) (W)Example D1 17.9 7.38 1.16 13.51 366 0.094 Example D2 18.4 5.79 1.1913.37 363 0.099 Example D3 19.4 5.15 1.18 13.15 363 0.099 Example D420.0 4.30 1.20 13.08 362 0.102 Example D5 22.4 2.88 1.19 12.64 358 0.090Comparative 10.4 3.92 1.08 11.82 364 0.087 Example D1 Comparative 10.52.97 1.11 11.87 360 0.080 Example D2 Comparative 15.8 3.53 1.11 12.06362 0.085 Example D3 Comparative 15.4 2.51 1.15 12.13 361 0.069 ExampleD4 Comparative 10.7 4.48 1.07 11.88 364 0.086 Example D5 Comparative19.3 1.82 1.21 12.56 361 0.059 Example D6

In Examples D1 to D5, the flake natural graphite adjusted to have aprescribed particle size was spheroidized while fine powder generatedduring the spheroidization was deposited on the base material and/orincorporated into the spheroidized particles, whereby the aboveinequality (1D) was successfully satisfied to provide a high capacityand excellent low-temperature output characteristics.

Fifth examples (Examples E) of the present invention will now bedescribed.

Preparation of Electrode Sheet

An electrode plate having an active material layer with an activematerial layer density of 1.50±0.03 g/cm³ was prepared using graphiteparticles of Examples or Comparative Examples. Specifically, 50.00±0.02g of a negative electrode material, 50.00±0.02 g (0.500 g on a solidsbasis) of a 1% by mass aqueous carboxymethylcellulose sodium saltsolution, and 1.00±0.05 g (0.5 g on a solids basis) of an aqueousdispersion of a styrene-butadiene rubber having a weight averagemolecular weight of 270,000 were stirred with a Keyence hybrid mixer for5 minutes, and the mixture was defoamed for 30 seconds to give a slurry.The slurry was applied to a 10-μm-thick copper foil, serving as acurrent collector, to a width of 10 cm using a small die coateravailable from Itochu Machining Co., Ltd. such that the negativeelectrode material adhered in an amount of 6.00±0.3 mg/cm² or 12.00±0.3mg/cm². The coated foil was roll-pressed using a roller having adiameter of 20 cm to adjust the density of the active material layer tobe 1.50±0.03 g/cm², thereby preparing an electrode sheet.

Production of Non-Aqueous Secondary Battery (2016 Coin Battery)

The electrode sheet prepared by the above-described method, to which thenegative electrode material adhered in an amount of 12.00±0.3 mg/cm²,was cut into a disk having a diameter of 12.5 mm, and lithium metal foilwas cut into a disk having a diameter of 14 mm to prepare a counterelectrode. A separator (made of a porous polyethylene film) was placedbetween the two electrodes, the separator being impregnated with anelectrolyte solution of 1 mol/L of LiPF₆ in a mixed solvent of ethylenecarbonate and ethyl methyl carbonate (volume ratio=3:7). In this manner,2016 coin batteries were produced.

Method of Producing Non-Aqueous Secondary Battery (Laminate Battery)

The electrode sheet prepared by the above-described method, to which thenegative electrode material adhered in an amount of 6.00±0.3 mg/cm², wascut to 4 cm×3 cm to prepare a negative electrode, and a positiveelectrode made of NMC was cut to the same area. The negative electrodeand the positive electrode were combined with a separator (made of aporous polyethylene film) placed therebetween. An electrolyte solutionof 1.2 mol/L of LiPF₆ in a mixed solvent of ethylene carbonate, ethylmethyl carbonate, and dimethyl carbonate (volume ratio=3:3:4) wasinjected in an amount of 250 μl to produce a laminate battery.

Method for Measuring Initial Discharge Capacity

Using the non-aqueous secondary battery (2016 coin battery) produced bythe above-described method, the capacity of the battery during chargingand discharging was measured by the following method.

The lithium counter electrode was charged to 5 mV at a current densityof 0.04 C and further charged at a constant voltage of 5 mV to a currentdensity of 0.005 C. The negative electrode was doped with lithium, andthen the lithium counter electrode was discharged to 1.5 V at a currentdensity of 0.08 C. Subsequently, a second charging and discharging wasperformed at the same current density. The discharge capacity at thesecond cycle was defined as an initial discharge capacity (1st dischargecapacity) of this battery.

Low-Temperature Output Characteristics

Using the laminate non-aqueous electrolyte secondary battery produced bythe method for producing a non-aqueous electrolyte secondary batterydescribed above, low-temperature output characteristics were measured bythe following method.

A non-aqueous electrolyte secondary battery that had yet to go through acharge and discharge cycle was subjected to an initial charge anddischarge that involves three cycles in a voltage range of 4.1 V to 3.0V at 25° C. and a current of 0.2 C (1 C is a current at which a ratedcapacity at a 1-hour rate discharge capacity is discharged in 1 hour,and so on) and two cycles in a voltage range of 4.2 V to 3.0 V at acurrent of 0.2 C (in charging, a constant-voltage charge at 4.2 V wasfurther performed for 2.5 hours).

Furthermore, charging was performed at a current of 0.2 C to an SOC of50%, and then constant-current discharging was performed in alow-temperature environment at −30° C. for 2 seconds at varying currentsof ⅛ C, ¼ C, ½ C, 1.5 C, and 2 C. The battery voltage drop at 2 secondsafter discharging under each condition was measured. From eachmeasurement, a current I that could be passed in 2 seconds when theupper limit charge voltage was 3 V was calculated, and a valuecalculated from the formula: 3×I (W) was defined as the low-temperatureoutput characteristics of each battery.

Average Particle Diameter d50; d50

The d50 was determined as a volume-based median diameter by suspending0.01 g of a carbon material in 10 mL of a 0.2% by mass aqueous solutionof a polyoxyethylene sorbitan monolaurate surfactant (Tween 20(registered trademark)), placing the suspension (a measurement sample)in a commercially available laser diffraction/scattering particle sizedistribution analyzer (e.g., LA-920 available from HORIBA, Ltd.),irradiating the measurement sample with ultrasonic waves of 28 kHz at apower of 60 W for 1 minute, and then performing a measurement with theanalyzer.

Average Particle Diameter d90; d90

d90 is a particle diameter corresponding to a cumulative total of 90%from the smallest particle, as measured on a volume basis.

Average Particle Diameter d10; d10

d10 is a particle diameter corresponding to a cumulative total of 10%from the smallest particle, as measured on a volume basis.

Tap Density

Using a powder density meter, the carbon material of the presentinvention was dropped through a sieve with openings of 300 μm into acylindrical tap cell with a diameter of 1.6 cm and a volume capacity of20 cm³ to fill up the cell, and then a tap with a stroke length of 10 mmwas given 1,000 times. The density calculated from the volume at thistime and the mass of the sample was defined as the tap density.

Specific Surface Area Determined by BET Method; SA (X_(e))

Using a surface area meter (TriStar II3020 available from MicromeriticsCorp.), a carbon material sample was preliminarily dried under anitrogen stream at 350° C. for 60 minutes, and then using anitrogen-helium mixed gas precisely regulated so as to have a nitrogenpressure of 0.3 relative to atmospheric pressure, a BET specific surfacearea was measured by a nitrogen adsorption BET multipoint methodaccording to a flowing gas method.

True Density: Y_(e)

The true density of a carbon material sample was measured by pycnometryusing a true density meter (MAT-7000 Auto True Denser available fromSeishin Enterprise Co., Ltd).

Example E1

A flake natural graphite having a d50 of 100 μm was crushed with amechanical crusher having a crushing rotor and a liner to give a flakenatural graphite having a d50 of 30 μm and a water content of 0.03% bymass. To 100 g of the resulting flake natural graphite, 6 g of agranulating agent of a paraffinic oil (liquid paraffin available fromWako Pure Chemical Industries, Ltd., first grade, physical properties at25° C.: viscosity=95 cP, contact angle=13.2°, surface tension=31.7 mN/m,r cos θ=30.9) was added and mixed with stirring. The sample obtained wasdisintegrated and mixed using a hammer mill (MF10 available from IKA) ata rotation speed of 3,000 rpm to give a flake natural graphite to whichthe granulating agent uniformly adhered. Using a Model NHS-1hybridization system available from Nara Machinery Co., Ltd., the flakenatural graphite to which the granulating agent uniformly adhered wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes while fine powder generated during the spheroidization wasdeposited on the base material and incorporated into the spheroidizedparticles, thereby providing a spheroidized natural graphite having ad50 of 19.4 μm. The spheroidized natural graphite and a coal-tar pitch,serving as an amorphous carbon precursor, were mixed and heat treated inan inert gas at 1,300° C., and then the burned product was disintegratedand classified to give a multi-layered carbon material made of graphiteparticles and an amorphous carbon combined with each other. The burningyield showed that the mass ratio of spheroidized graphite particle toamorphous carbon (spheroidized graphite particle/amorphous carbon) ofthe multi-layered carbon material was 1:0.03. Using the measurementmethods described above, d50, d90, d10, SA, Tap, true density, initialdischarge capacity, and low-temperature output characteristics weremeasured. The results are shown in Table 1E.

Example E2

The spheroidized natural graphite obtained in Example E1 and a coal-tarpitch, serving as an amorphous carbon precursor, were mixed and heattreated in an inert gas at 1,300° C., and then the burned product wasdisintegrated and classified to give a multi-layered carbon materialmade of graphite particles and an amorphous carbon combined with eachother. The burning yield showed that the mass ratio of spheroidizedgraphite particle to amorphous carbon (spheroidized graphiteparticle/amorphous carbon) of the multi-layered carbon material was1:0.042. The results of the measurements made in the same manner as inExample E1 are shown in Table 1E.

Example E3

The spheroidized natural graphite obtained in Example E1 and a coal-tarpitch, serving as an amorphous carbon precursor, were mixed and heattreated in an inert gas at 1,300° C., and then the burned product wasdisintegrated and classified to give a multi-layered carbon materialmade of graphite particles and an amorphous carbon combined with eachother. The burning yield showed that the mass ratio of spheroidizedgraphite particle to amorphous carbon (spheroidized graphiteparticle/amorphous carbon) of the multi-layered carbon material was1:0.05. The results of the measurements made in the same manner as inExample E1 are shown in Table 1E.

Example E4

The spheroidized natural graphite obtained in Example E1 and a coal-tarpitch, serving as an amorphous carbon precursor, were mixed and heattreated in an inert gas at 1,300° C., and then the burned product wasdisintegrated and classified to give a multi-layered carbon materialmade of graphite particles and an amorphous carbon combined with eachother. The burning yield showed that the mass ratio of spheroidizedgraphite particle to amorphous carbon (spheroidized graphiteparticle/amorphous carbon) of the multi-layered carbon material was1:0.065. The results of the measurements made in the same manner as inExample E1 are shown in Table 1E.

Example E5

The spheroidized natural graphite obtained in Example E1 and a coal-tarpitch, serving as an amorphous carbon precursor, were mixed and heattreated in an inert gas at 1,300° C., and then the burned product wasdisintegrated and classified to give a multi-layered carbon materialmade of graphite particles and an amorphous carbon combined with eachother. The burning yield showed that the mass ratio of spheroidizedgraphite particle to amorphous carbon (spheroidized graphiteparticle/amorphous carbon) of the multi-layered carbon material was1:0.10. The results of the measurements made in the same manner as inExample E1 are shown in Table 1E.

Example E6

A flake natural graphite having a d50 of 100 μm was crushed with amechanical crusher having a crushing rotor and a liner to give a flakenatural graphite having a d50 of 6 μm and a water content of 0.08% bymass. To 100 g of the resulting flake natural graphite, 12 g of agranulating agent of a paraffinic oil (liquid paraffin available fromWako Pure Chemical Industries, Ltd., first grade, physical properties at25° C.: viscosity=95 cP, contact angle=13.2°, surface tension=31.7 mN/m,r cos θ=30.9) was added and mixed with stirring. The sample obtained wasdisintegrated and mixed using a hammer mill (MF10 available from IKA) ata rotation speed of 3,000 rpm to give a flake natural graphite to whichthe granulating agent uniformly adhered. Using a Model NHS-1hybridization system available from Nara Machinery Co., Ltd., the flakenatural graphite to which the granulating agent uniformly adhered wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes while fine powder generated during the spheroidization wasdeposited on the base material and incorporated into the spheroidizedparticles, thereby providing a spheroidized natural graphite having ad50 of 9.2 μm. The spheroidized natural graphite and a coal-tar pitch,serving as an amorphous carbon precursor, were mixed and heat treated inan inert gas at 1,300° C., and then the burned product was disintegratedand classified to give a multi-layered carbon material made of graphiteparticles and an amorphous carbon combined with each other. The burningyield showed that the mass ratio of spheroidized graphite particle toamorphous carbon (spheroidized graphite particle/amorphous carbon) ofthe multi-layered carbon material was 1:0.065. The results of themeasurements made in the same manner as in Example E1 are shown in Table1E.

Example E7

A flake natural graphite having a d50 of 100 μm was crushed with amechanical crusher having a crushing rotor and a liner to give a flakenatural graphite having a d50 of 6 μm and a water content of 0.08% bymass. To 100 g of the resulting flake natural graphite, 12 g of agranulating agent of a paraffinic oil (liquid paraffin available fromWako Pure Chemical Industries, Ltd., first grade, physical properties at25° C.: viscosity=95 cP, contact angle=13.2°, surface tension=31.7 mN/m,r cos θ=30.9) was added and mixed with stirring. The sample obtained wasdisintegrated and mixed using a hammer mill (MF10 available from IKA) ata rotation speed of 3,000 rpm to give a flake natural graphite to whichthe granulating agent uniformly adhered. Using a Model NHS-1hybridization system available from Nara Machinery Co., Ltd., the flakenatural graphite to which the granulating agent uniformly adhered wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes while fine powder generated during the spheroidization wasdeposited on the base material and incorporated into the spheroidizedparticles, thereby providing a spheroidized natural graphite having ad50 of 9.2 μm. The spheroidized natural graphite and a coal-tar pitch,serving as an amorphous carbon precursor, were mixed and heat treated inan inert gas at 1,300° C., and then the burned product was disintegratedand classified to give a multi-layered carbon material made of graphiteparticles and an amorphous carbon combined with each other. The burningyield showed that the mass ratio of spheroidized graphite particle toamorphous carbon (spheroidized graphite particle/amorphous carbon) ofthe multi-layered carbon material was 1:0.1. The results of themeasurements made in the same manner as in Example E1 are shown in Table1E.

Comparative Example E1

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite and flake graphite fine powder generated duringthe spheroidization that were not deposited on the base material orincorporated. This sample was classified to remove the flake graphitefine powder, thereby providing a spheroidized graphite having a d50 of10.8 μm. The spheroidized natural graphite and a coal-tar pitch, servingas an amorphous carbon precursor, were mixed and heat treated in aninert gas at 1,300° C., and then the burned product was disintegratedand classified to give a multi-layered carbon material made of graphiteparticles and an amorphous carbon combined with each other. The burningyield showed that the mass ratio of spheroidized graphite particle toamorphous carbon (spheroidized graphite particle/amorphous carbon) ofthe multi-layered carbon material was 1:0.02. The results of themeasurements made in the same manner as in Example E1 are shown in Table1E.

Comparative Example E2

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite and flake graphite fine powder generated duringthe spheroidization that were not deposited on the base material orincorporated. This sample was classified to remove the flake graphitefine powder, thereby providing a spheroidized graphite having a d50 of10.8 μm. The spheroidized natural graphite and a coal-tar pitch, servingas an amorphous carbon precursor, were mixed and heat treated in aninert gas at 1,300° C., and then the burned product was disintegratedand classified to give a multi-layered carbon material made of graphiteparticles and an amorphous carbon combined with each other. The burningyield showed that the mass ratio of spheroidized graphite particle toamorphous carbon (spheroidized graphite particle/amorphous carbon) ofthe multi-layered carbon material was 1:0.04. The results of themeasurements made in the same manner as in Example E1 are shown in Table1E.

Comparative Example E3

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 3minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite and flake graphite fine powder generated duringthe spheroidization that were not deposited on the base material orincorporated. This sample was classified to remove the flake graphitefine powder, thereby providing a spheroidized graphite having a d50 of15.7 μm. The spheroidized natural graphite and a coal-tar pitch, servingas an amorphous carbon precursor, were mixed and heat treated in aninert gas at 1,300° C., and then the burned product was disintegratedand classified to give a multi-layered carbon material made of graphiteparticles and an amorphous carbon combined with each other. The burningyield showed that the mass ratio of spheroidized graphite particle toamorphous carbon (spheroidized graphite particle/amorphous carbon) ofthe multi-layered carbon material was 1:0.015. The results of themeasurements made in the same manner as in Example E1 are shown in Table1E.

Comparative Example E4

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 3minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite and flake graphite fine powder generated duringthe spheroidization that were not deposited on the base material orincorporated. This sample was classified to remove the flake graphitefine powder, thereby providing a spheroidized graphite having a d50 of15.7 μm. The spheroidized natural graphite and a coal-tar pitch, servingas an amorphous carbon precursor, were mixed and heat treated in aninert gas at 1,300° C., and then the burned product was disintegratedand classified to give a multi-layered carbon material made of graphiteparticles and an amorphous carbon combined with each other. The burningyield showed that the mass ratio of spheroidized graphite particle toamorphous carbon (spheroidized graphite particle/amorphous carbon) ofthe multi-layered carbon material was 1:0.04. The results of themeasurements made in the same manner as in Example E1 are shown in Table1E.

Comparative Example E5

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite and flake graphite fine powder generated duringthe spheroidization that were not deposited on the base material orincorporated. This sample was classified to remove the flake graphitefine powder, thereby providing a spheroidized graphite having a d50 of10.8 μm. The spheroidized natural graphite and a coal-tar pitch, servingas an amorphous carbon precursor, were mixed and heat treated in aninert gas at 1,300° C., and then the burned product was disintegratedand classified to give a multi-layered carbon material made of graphiteparticles and an amorphous carbon combined with each other. The burningyield showed that the mass ratio of spheroidized graphite particle toamorphous carbon (spheroidized graphite particle/amorphous carbon) ofthe multi-layered carbon material was 1:0.013. The results of themeasurements made in the same manner as in Example E1 are shown in Table1E.

Comparative Example E6

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 3minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite and flake graphite fine powder generated duringthe spheroidization that were not deposited on the base material orincorporated. This sample was classified to remove the flake graphitefine powder, thereby providing a spheroidized graphite having a d50 of19.5 μm. The spheroidized natural graphite and a coal-tar pitch, servingas an amorphous carbon precursor, were mixed and heat treated in aninert gas at 1,300° C., and then the burned product was disintegratedand classified to give a multi-layered carbon material made of graphiteparticles and an amorphous carbon combined with each other. The burningyield showed that the mass ratio of spheroidized graphite particle toamorphous carbon (spheroidized graphite particle/amorphous carbon) ofthe multi-layered carbon material was 1:0.075. The results of themeasurements made in the same manner as in Example E1 are shown in Table1E.

TABLE 1E Y_(e): Initial Low- X_(e): True Discharge Temperture SA DensityY_(e) − d50 d90/ Tap Capacity Output (m²/g) (g/cm³) 0.01X_(e) (μm) d10(g/cm³) (mAH/g) Characteristics (W) Example E1 7.38 2.25 2.17 17.9 3.21.16 366 0.094 Example E2 5.79 2.24 2.18 18.4 3.1 1.19 363 0.098 ExampleE3 5.15 2.24 2.19 19.4 3.0 1.18 363 0.099 Example E4 4.30 2.23 2.19 20.02.8 1.20 362 0.102 Example E5 2.88 2.22 2.19 22.4 3.1 1.19 358 0.090Example E6 8.69 2.23 2.14 8.9 2.8 0.94 361 0.107 Example E7 6.21 2.222.15 10.2 3.1 0.80 356 0.106 Comparative 3.92 2.25 2.21 10.4 2.3 1.08364 0.087 Example E1 Comparative 2.97 2.24 2.21 10.6 2.1 1.11 360 0.080Example E2 Comparative 3.53 2.25 2.22 15.8 2.4 1.11 362 0.085 Example E3Comparative 2.51 2.24 2.21 15.4 2.2 1.15 361 0.069 Example E4Comparative 4.48 2.25 2.21 10.5 2.2 1.07 364 0.086 Example E5Comparative 1.82 2.23 2.21 19.3 2.5 1.21 361 0.059 Example E6

In Examples E1 to E7, the flake natural graphite adjusted to have aprescribed particle size was spheroidized while fine powder generatedduring the spheroidization was deposited on the base material and/orincorporated into the spheroidized particles, whereby the aboveinequality (1E) was successfully satisfied to provide a high capacityand excellent low-temperature output characteristics.

Sixth examples (Examples F) of the present invention will now bedescribed.

In Examples F, physical properties and characteristics of carbonmaterials produced were measured by the following methods.

Preparation of Electrode Sheet

An electrode plate having an active material layer with an activematerial layer density of 1.35±0.03 g/cm³ was prepared using graphiteparticles of Examples or Comparative Examples. Specifically, 50.00±0.02g of a negative electrode material, 50.00±0.02 g (0.500 g on a solidsbasis) of a 1% by mass aqueous carboxymethylcellulose sodium saltsolution, and 1.00±0.05 g (0.5 g on a solids basis) of an aqueousdispersion of a styrene-butadiene rubber having a weight averagemolecular weight of 270,000 were stirred with a Keyence hybrid mixer for5 minutes, and the mixture was defoamed for 30 seconds to give a slurry.

The slurry was applied to a 10-μm-thick copper foil, serving as acurrent collector, to a width of 10 cm using a small die coateravailable from Itochu Machining Co., Ltd. such that the negativeelectrode material adhered in an amount of 6.00±0.3 mg/cm². The coatedfoil was roll-pressed using a roller having a diameter of 20 cm toadjust the density of the active material layer to be 1.35±0.03 g/cm³,thereby preparing an electrode sheet.

Production of Non-Aqueous Secondary Battery (2016 Coin Battery)

The electrode sheet prepared by the above-described method, to which thenegative electrode material adhered in an amount of 12.00±0.3 mg/cm²,was cut into a disk having a diameter of 12.5 mm, and lithium metal foilwas cut into a disk having a diameter of 14 mm to prepare a counterelectrode. A separator (made of a porous polyethylene film) was placedbetween the two electrodes, the separator being impregnated with anelectrolyte solution of 1 mol/L of LiPF₆ in a mixed solvent of ethylenecarbonate and ethyl methyl carbonate (volume ratio=3:7). In this manner,2016 coin batteries were produced.

Method for Measuring Initial Discharge Capacity

Using the non-aqueous secondary battery (2016 coin battery) produced bythe above-described method, the capacity of the battery during chargingand discharging was measured by the following method.

The lithium counter electrode was charged to 5 mV at a current densityof 0.04 C and further charged at a constant voltage of 5 mV to a currentdensity of 0.005 C. The negative electrode was doped with lithium, andthen the lithium counter electrode was discharged to 1.5 V at a currentdensity of 0.08 C. Subsequently, a second charging and discharging wasperformed at the same current density. The discharge capacity at thesecond cycle was defined as an initial discharge capacity (1st dischargecapacity) of this battery.

Method of Producing Non-Aqueous Secondary Battery (Laminate Battery)

The electrode sheet prepared by the above-described method was cut to 4cm×3 cm to prepare a negative electrode, and a positive electrode madeof NMC was cut to the same area. The negative electrode and the positiveelectrode were combined with a separator (made of a porous polyethylenefilm) placed therebetween. An electrolyte solution of 1.2 mol/L of LiPF₆in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, anddimethyl carbonate (volume ratio=3:3:4) was injected in an amount of 200μL to produce a laminate battery.

Low-Temperature Output Characteristics

Using the laminate non-aqueous electrolyte secondary battery produced bythe method for producing a non-aqueous electrolyte secondary batterydescribed above, low-temperature output characteristics were measured bythe following method.

A non-aqueous electrolyte secondary battery that had yet to go through acharge and discharge cycle was subjected to an initial charge anddischarge that involves three cycles in a voltage range of 4.1 V to 3.0V at 25° C. and a current of 0.2 C (1 C is a current at which a ratedcapacity at a 1-hour rate discharge capacity is discharged in 1 hour,and so on) and two cycles in a voltage range of 4.2 V to 3.0 V at acurrent of 0.2 C (in charging, a constant-voltage charge at 4.2 V wasfurther performed for 2.5 hours).

Furthermore, charging was performed at a current of 0.2 C to an SOC of50%, and then constant-current discharging was performed in alow-temperature environment at −30° C. for 2 seconds at varying currentsof ⅛ C, ¼ C, ½ C, 1.5 C, and 2 C. The battery voltage drop at 2 secondsafter discharging under each condition was measured. From eachmeasurement, a current I that could be passed in 2 seconds when theupper limit charge voltage was 3 V was calculated, and a valuecalculated from the formula: 3×I (W) was defined as the low-temperatureoutput characteristics of each battery.

Average Value, Standard Deviation (σ_(R)), and Raman R₁₅ Value ofMicroscopic Raman R Values

Using a Raman spectroscope (Nicolet Almega XR available from ThermoFisher Scientific K.K.), Raman microspectroscopy was performed under thefollowing conditions to determine the average value and the standarddeviation (σ_(R)) of microscopic Raman R values.

Target particles were gravity-dropped onto a sample stage, and Ramanmicrospectroscopy was performed with the surface of the target flat.

Excitation wavelength: 532 nm

Laser power on sample: 1 mW or less

Resolution: 10 cm⁻¹

Irradiation area: 1 μm □

Measurement range: 400 cm to 4,000 cm

Measurement of peak intensity: straight baseline subtraction in therange of about 1,100 cm⁻¹ to 1,750 cm⁻¹

Method for calculating Raman R value: In a spectrum after straightbaseline subtraction, a peak intensity I_(A) at the peak top of a peakP_(A) near 1,580 cm⁻¹ and a peak intensity I_(B) at the peak top of apeak P_(B) near 1,360 cm⁻¹ were read to calculate an R value(I_(B)/I_(A)), and the average value and the standard deviation (σ_(R))were calculated.

Method of calculating Raman R₍₁₅₎ value (%): the number of compositecarbon materials having a microscopic Raman R value of 0.15 or lessamong 30 randomly selected composite carbon materials/30×100

d50

The d50 was determined as a volume-based median diameter by suspending0.01 g of a carbon material in 10 mL of a 0.2% by mass aqueous solutionof a polyoxyethylene sorbitan monolaurate surfactant (Tween 20(registered trademark)), placing the suspension (a measurement sample)in a commercially available laser diffraction/scattering particle sizedistribution analyzer (e.g., LA-920 available from HORIBA, Ltd.),irradiating the measurement sample with ultrasonic waves of 28 kHz at apower of 60 W for 1 minute, and then performing a measurement with theanalyzer.

Mode Pore Diameter (PD) in Pore Diameter Range of 0.01 μm to 1 μm, HalfWidth at Half Maximum of Pore Distribution (Log (Nm)), Cumulative PoreVolume at Pore Diameters in Range of 0.01 μm to 1 μm, and Total PoreVolume

The measurement by mercury intrusion was carried out using a mercuryporosimeter (Autopore 9520 available from Micromeritics Corp). Around0.2 g of a sample (negative electrode material) was weighed into apowder cell, and the cell was sealed. The cell was subjected to adegassing pretreatment at room temperature under vacuum (50 μmHg orlower) for 10 minutes, and then the pressure in the cell was reducedstepwise to 4 psia. Mercury was introduced into the cell, and thepressure was increased stepwise from 4 psia to 40,000 psia and thenreduced to 25 psia. From the mercury intrusion curve obtained, a poredistribution was calculated using the Washburn equation. The calculationwas made assuming that the surface tension of mercury was 485 dyne/cm,and the contact angle was 140°.

From the pore distribution obtained, a mode pore diameter (PD) in a porediameter range of 0.01 μm to 1 μm, a cumulative pore volume at porediameters in a range of 0.01 μm to 1 μm, and a total pore volume werecalculated. The half width at half maximum of pore distribution (log(nm)) is defined as a half width at half maximum at a micropore side ofa peak in a pore diameter range of 0.01 μm to 1 μm in the poredistribution (nm) with the horizontal axis expressed in common logarithm(log (nm)).

BET Specific Surface Area (SA)

Using a surface area meter (Gemini 2360 specific surface area analyzeravailable from Shimadzu Corporation), a carbon material sample waspreliminarily vacuum dried under a nitrogen stream at 100° C. for 3hours and then cooled to liquid nitrogen temperature, and using anitrogen-helium mixed gas precisely regulated so as to have a nitrogenpressure of 0.3 relative to atmospheric pressure, a BET specific surfacearea was measured by a nitrogen adsorption BET multipoint methodaccording to a flowing gas method.

Tap Density (Tap)

Using a powder density meter, the carbon material of the presentinvention was dropped through a sieve with openings of 300 μm into acylindrical tap cell with a diameter of 1.6 cm and a volume capacity of20 cm³ to fill up the cell, and then a tap with a stroke length of 10 mmwas given 1,000 times. The density calculated from the volume at thistime and the mass of the sample was defined as the tap density.

Example F1

A flake natural graphite having a d50 of 100 μm was crushed with a dryair-flow crusher to give a flake natural graphite having a d50 of 6 μmand a Tap of 0.13 g/cm³. To 100 g of the resulting flake naturalgraphite, 12 g of a granulating agent of a paraffinic oil (liquidparaffin available from Wako Pure Chemical Industries, Ltd., firstgrade, physical properties at 25° C.: viscosity=95 cP, contactangle=13.2°, surface tension=31.7 mN/m, r cos θ=30.9) was added andmixed with stirring. The sample obtained was disintegrated and mixedusing a hammer mill (MF10 available from IKA) at a rotation speed of3,000 rpm to give a flake natural graphite to which the granulatingagent uniformly adhered. Using a Model NHS-1 hybridization systemavailable from Nara Machinery Co., Ltd., the flake natural graphite towhich the granulating agent uniformly adhered was mechanicallyspheroidized at a rotor peripheral speed of 85 m/sec for 10 minuteswhile the flake natural graphites were made to adhere to each other andfine powder generated during the spheroidization was deposited on thebase material and incorporated into the spheroidized particles, therebyproviding a spheroidized graphite having a d50 of 9.2 μm, a Tap densityof 0.71 g/cm³, a PD of 0.09 μm, a PD/d50 of 0.99, and a cumulative porevolume at pore diameters in a range of 0.01 μm to 1 μm of 0.16 mL/g. Thespheroidized graphite powder obtained and a coal-tar pitch having aresidual carbon ratio of 40% and a density of 1.2 g/cm³, serving as anamorphous carbon precursor, were mixed while being heated to atemperature equal to or higher than the softening point of the coal-tarpitch, and heat treated in an inert gas at 1,300° C., after which theburned product was disintegrated and classified to give a multi-layeredcarbon material made of graphite particles and an amorphous carboncombined with each other. The burning yield showed that the mass ratioof spheroidized graphite particle to amorphous carbon (spheroidizedgraphite particle/amorphous carbon) of the multi-layered carbon materialwas 1:0.07. Using the measurement methods described above, d50, SA, Tapdensity, average value of microscopic Raman R values, σ_(R), Raman R₁₅value, discharge capacity, and low-temperature output characteristicswere measured. The results are shown in Tables 1F and 2F.

Example F2

A flake natural graphite having a d50 of 100 μm was crushed with a dryswirl-flow crusher to give a flake natural graphite having a d50 of 9 μmand a Tap of 0.42 g/cm³. To 100 g of the resulting flake naturalgraphite, 12 g of a granulating agent of a paraffinic oil (liquidparaffin available from Wako Pure Chemical Industries, Ltd., firstgrade, physical properties at 25° C.: viscosity=95 cP, contactangle=13.2°, surface tension=31.7 mN/m, r cos θ=30.9) was added andmixed with stirring. The sample obtained was disintegrated and mixedusing a hammer mill (MF10 available from IKA) at a rotation speed of3,000 rpm to give a flake natural graphite to which the granulatingagent uniformly adhered. Using a Model NHS-1 hybridization systemavailable from Nara Machinery Co., Ltd., the flake natural graphite towhich the granulating agent uniformly adhered was mechanicallyspheroidized at a rotor peripheral speed of 85 m/sec for 10 minuteswhile the flake natural graphites were made to adhere to each other andfine powder generated during the spheroidization was deposited on thebase material and incorporated into the spheroidized particles, therebyproviding a spheroidized graphite having a d50 of 12.7 μm, a Tap densityof 0.87 g/cm³, a PD of 0.09 μm, a PD/d50 of 0.71, and a cumulative porevolume at pore diameters in a range of 0.01 μm to 1 μm of 0.16 mL/g. Thespheroidized graphite powder obtained and a coal-tar pitch having aresidual carbon ratio of 40% and a density of 1.2 g/cm³, serving as anamorphous carbon precursor, were mixed while being heated to atemperature equal to or higher than the softening point of the coal-tarpitch, and heat treated in an inert gas at 1,300° C., after which theburned product was disintegrated and classified to give a multi-layeredcarbon material made of graphite particles and an amorphous carboncombined with each other. The burning yield showed that the mass ratioof spheroidized graphite particle to amorphous carbon (spheroidizedgraphite particle/amorphous carbon) of the multi-layered carbon materialwas 1:0.08. The results of the measurements made in the same manner asin Example F1 are shown in Table 1F.

Example F3

A multi-layered carbon material was obtained in the same manner as inExample 2 except that a coal tar having a residual carbon ratio of 28%and a density of 1.2 g/cm³ was used as an amorphous carbon precursor.The burning yield showed that the mass ratio of spheroidized graphiteparticle to amorphous carbon (spheroidized graphite particle/amorphouscarbon) of the multi-layered carbon material was 1:0.08. The results ofthe measurements made in the same manner as in Example F1 are shown inTable 1F.

Comparative Example F1

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite and flake graphite fine powder generated duringthe spheroidization that were not deposited on the base material orincorporated. This sample was classified to remove the flake graphitefine powder, thereby providing a spheroidized graphite having a d50 of10.8 μm, a Tap density of 0.88 g/cm³, a PD of 0.36 μm, a PD/d50 of 3.27,and a cumulative pore volume at pore diameters in a range of 0.01 μm to1 μm of 0.14 mL/g.

The spheroidized graphite powder obtained and a coal tar having aresidual carbon ratio of 28% and a density of 1.2 g/cm³, serving as anamorphous carbon precursor, were mixed while being heated to atemperature equal to or higher than the softening point of the coal-tarpitch, and heat treated in an inert gas at 1,300° C., after which theburned product was disintegrated and classified to give a multi-layeredcarbon material made of graphite particles and an amorphous carboncombined with each other. The burning yield showed that the mass ratioof spheroidized graphite particle to amorphous carbon (spheroidizedgraphite particle/amorphous carbon) of the multi-layered carbon materialwas 1:0.07. The results of the measurements made in the same manner asin Example F1 are shown in Table 1F.

Comparative Example F2

A multi-layered carbon material was obtained in the same manner as inComparative Example 1 except that a coal-tar pitch having a residualcarbon ratio of 40% and a density of 1.2 g/cm³ was used as an amorphouscarbon precursor. The burning yield showed that the mass ratio ofspheroidized graphite particle to amorphous carbon (spheroidizedgraphite particle/amorphous carbon) of the multi-layered carbon materialwas 1:0.07. The results of the measurements made in the same manner asin Example F1 are shown in Table 1F.

Example F4

A flake natural graphite having a d50 of 100 μm was crushed with amechanical crusher having a crushing rotor and a liner to give a flakenatural graphite having a d50 of 30 μm. To 100 g of the resulting flakenatural graphite, 4 g of a granulating agent of a paraffinic oil (liquidparaffin available from Wako Pure Chemical Industries, Ltd., firstgrade, physical properties at 25° C.: viscosity=95 cP, contactangle=13.2°, surface tension=31.7 mN/m, r cos θ=30.9) was added andmixed with stirring. The sample obtained was disintegrated and mixedusing a hammer mill (MF10 available from IKA) at a rotation speed of3,000 rpm to give a flake natural graphite to which the granulatingagent uniformly adhered. Using a Model NHS-1 hybridization systemavailable from Nara Machinery Co., Ltd., the flake natural graphite towhich the granulating agent uniformly adhered was mechanicallyspheroidized at a rotor peripheral speed of 85 m/sec for 10 minuteswhile fine powder generated during the spheroidization was deposited onthe base material and incorporated into the spheroidized particles,thereby providing a spheroidized natural graphite having a d50 of 16.3μm, a Tap density of 1.03 g/cm³, a PD of 0.22 μm, a PD/d50 of 1.33, anda cumulative pore volume at pore diameters in a range of 0.01 μm to 1 μmof 0.10 mL/g. The spheroidized graphite powder and a coal-tar pitchhaving a residual carbon ratio of 40% and a density of 1.2 g/cm³,serving as an amorphous carbon precursor, were mixed while being heatedto a temperature equal to or higher than the softening point of thecoal-tar pitch, and heat treated in an inert gas at 1,300° C., afterwhich the burned product was disintegrated and classified to give amulti-layered carbon material made of graphite particles and anamorphous carbon combined with each other. The burning yield showed thatthe mass ratio of spheroidized graphite particle to amorphous carbon(spheroidized graphite particle/amorphous carbon) of the multi-layeredcarbon material was 1:0.04. The results of the measurements made in thesame manner as in Example F1 are shown in Table 1F.

Example F5

A multi-layered carbon material was obtained in the same manner as inExample 5 except that a coal tar having a residual carbon ratio of 28%and a density of 1.2 g/cm³ was used as an amorphous carbon precursor.The burning yield showed that the mass ratio of spheroidized graphiteparticle to amorphous carbon (spheroidized graphite particle/amorphouscarbon) of the multi-layered carbon material was 1:0.04. The results ofthe measurements made in the same manner as in Example F1 are shown inTable 1F.

Comparative Example F3

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 3minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite and flake graphite fine powder generated duringthe spheroidization that were not deposited on the base material orincorporated. This sample was classified to remove the flake graphitefine powder, thereby providing a spheroidized graphite having a d50 of15.7 μm, a Tap density of 1.02 g/cm³, a PD of 0.36 μm, a PD/d50 of 2.31,and a cumulative pore volume at pore diameters in a range of 0.01 μm to1 μm of 0.13 mL/g. The spheroidized graphite powder obtained and apetroleum-derived heavy oil having a residual carbon ratio of 18% and adensity of 1.1 g/cm³, serving as an amorphous carbon precursor, weremixed while being heated to a temperature equal to or higher than thesoftening point of the coal-tar pitch, and heat treated in an inert gasat 1,300° C., after which the burned product was disintegrated andclassified to give a multi-layered carbon material made of graphiteparticles and an amorphous carbon combined with each other. The burningyield showed that the mass ratio of spheroidized graphite particle toamorphous carbon (spheroidized graphite particle/amorphous carbon) ofthe multi-layered carbon material was 1:0.04. The results of themeasurements made in the same manner as in Example F1 are shown in Table1F.

TABLE 1F Low- Temperature Output Average Raman Characteristics IntitialRaman R₁₅ (Comparative Discharge d50 Tap R value Example Capacity (μm)SA (m²/g) (g/cm³) value σ_(R) (%) F1 = 100) (mAh/g) Example 9.4 8.7 0.940.28 0.077 3.3 139 362 F1 Example F2 11.8 7.1 1.02 0.24 0.056 3.3 147359 Example 12.2 7.6 0.78 0.28 0.088 10.0 126 359 F3 Comparative 11.43.1 1.04 0.33 0.150 6.7 100 362 Example F1 Comparative 11.3 3.1 1.020.27 0.126 13.3 107 362 Example F2 Example 15.8 4.8 1.22 0.22 0.058 13.3121 363 F4 Example 15.6 5.2 1.16 0.23 0.084 20.0 122 363 F5 Comparative16.8 3.3 1.16 0.28 0.107 20.0 107 363 Example F3

In Examples F1 to F5, a carbon material having specific intra-particlepores was mixed with an appropriate amount of a specific carbonaceousmaterial precursor, whereby the standard deviation (σ_(R)) ofmicroscopic Raman R values was controlled within the prescribed range toprovide excellent low-temperature output characteristics. In Examples F1to F3, the percentage of R values of 0.15 or less was in the preferredrange, thus leading to particularly excellent low-temperature outputcharacteristics. By contrast, in Comparative Examples F1 to F3, wherethe σ_(R) was outside the prescribed range, degraded low-temperatureoutput characteristics were provided.

Seventh examples (Examples G) of the present invention will now bedescribed.

In Examples G, physical properties of negative electrode materialsproduced were measured by the following methods.

Preparation of Electrode Sheet

An electrode plate having an active material layer with an activematerial layer density of 1.50±0.03 g/cm³ was prepared using graphiteparticles of Examples or Comparative Examples. Specifically, 50.00±0.02g of a negative electrode material, 50.00±0.02 g (0.500 g on a solidsbasis) of a 1% by mass aqueous carboxymethylcellulose sodium saltsolution, and 1.00±0.05 g (0.5 g on a solids basis) of an aqueousdispersion of a styrene-butadiene rubber having a weight averagemolecular weight of 270,000 were stirred with a Keyence hybrid mixer for5 minutes, and the mixture was defoamed for 30 seconds to give a slurry.

The slurry was applied to a 10-μm-thick copper foil, serving as acurrent collector, to a width of 10 cm using a small die coateravailable from Itochu Machining Co., Ltd. such that the negativeelectrode material adhered in an amount of 6.00±0.3 mg/cm². The coatedfoil was roll-pressed using a roller having a diameter of 20 cm toadjust the density of the active material layer to be 1.35±0.03 g/cm³,thereby preparing an electrode sheet.

Production of Non-Aqueous Secondary Battery (2016 Coin Battery)

The electrode sheet prepared by the above-described method, to which thenegative electrode material adhered in an amount of 12.00±0.3 mg/cm²,was cut into a disk having a diameter of 12.5 mm, and lithium metal foilwas cut into a disk having a diameter of 14 mm to prepare a counterelectrode. A separator (made of a porous polyethylene film) was placedbetween the two electrodes, the separator being impregnated with anelectrolyte solution of 1 mol/L of LiPF₆ in a mixed solvent of ethylenecarbonate and ethyl methyl carbonate (volume ratio=3:7). In this manner,2016 coin batteries were produced.

Method for Measuring Initial Discharge Capacity

Using the non-aqueous secondary battery (2016 coin battery) produced bythe above-described method, the capacity of the battery during chargingand discharging was measured by the following method.

The lithium counter electrode was charged to 5 mV at a current densityof 0.04 C and further charged at a constant voltage of 5 mV to a currentdensity of 0.005 C. The negative electrode was doped with lithium, andthen the lithium counter electrode was discharged to 1.5 V at a currentdensity of 0.08 C. Subsequently, a second charging and discharging wasperformed at the same current density. The discharge capacity at thesecond cycle was defined as an initial discharge capacity (1st dischargecapacity) of this battery.

Method of Producing Non-Aqueous Secondary Battery (Laminate Battery)

The electrode sheet prepared by the above-described method, to which thenegative electrode material adhered in an amount of 6.00±0.3 mg/cm², wascut to 4 cm×3 cm to prepare a negative electrode, and a positiveelectrode made of NMC was cut to the same area. The negative electrodeand the positive electrode were combined with a separator (made of aporous polyethylene film) placed therebetween. An electrolyte solutionof 1.2 mol/L of LiPF₆ in a mixed solvent of ethylene carbonate, ethylmethyl carbonate, and dimethyl carbonate (volume ratio=3:3:4) wasinjected in an amount of 250 μl to produce a laminate battery.

Low-Temperature Output Characteristics

Using the laminate non-aqueous electrolyte secondary battery produced bythe method for producing a non-aqueous electrolyte secondary batterydescribed above, low-temperature output characteristics were measured bythe following method.

A non-aqueous electrolyte secondary battery that had yet to go through acharge and discharge cycle was subjected to an initial charge anddischarge that involves three cycles in a voltage range of 4.1 V to 3.0V at 25° C. and a current of 0.2 C (1 C is a current at which a ratedcapacity at a 1-hour rate discharge capacity is discharged in 1 hour,and so on) and two cycles in a voltage range of 4.2 V to 3.0 V at acurrent of 0.2 C (in charging, a constant-voltage charge at 4.2 V wasfurther performed for 2.5 hours).

Furthermore, charging was performed at a current of 0.2 C to an SOC of50%, and then constant-current discharging was performed in alow-temperature environment at −30° C. for 2 seconds at varying currentsof ⅛ C, ¼ C, ½ C, 1.5 C, and 2 C. The battery voltage drop at 2 secondsafter discharging under each condition was measured. From eachmeasurement, a current I that could be passed in 2 seconds when theupper limit charge voltage was 3 V was calculated, and a valuecalculated from the formula: 3×I (W) was defined as the low-temperatureoutput characteristics of each battery.

Average Particle Diameter d50; d50

The d50 was determined as a volume-based median diameter by suspending0.01 g of a carbon material in 10 mL of a 0.2% by mass aqueous solutionof a polyoxyethylene sorbitan monolaurate surfactant (Tween 20(registered trademark)), placing the suspension (a measurement sample)in a commercially available laser diffraction/scattering particle sizedistribution analyzer (e.g., LA-920 available from HORIBA, Ltd.),irradiating the measurement sample with ultrasonic waves of 28 kHz at apower of 60 W for 1 minute, and then performing a measurement with theanalyzer.

Tap Density; Tap

Using a powder density meter, the carbon material of the presentinvention was dropped through a sieve with openings of 300 μm into acylindrical tap cell with a diameter of 1.6 cm and a volume capacity of20 cm³ to fill up the cell, and then a tap with a stroke length of 10 mmwas given 1,000 times. The density calculated from the volume at thistime and the mass of the sample was defined as the tap density.

Specific Surface Area Determined by BET Method; SA

Using a surface area meter (fully automatic surface area analyzeravailable from Ohkura Riken Co., Ltd.), a carbon material sample waspreliminarily dried under a nitrogen stream at 350° C. for 15 minutes,and then using a nitrogen-helium mixed gas precisely regulated so as tohave a nitrogen pressure of 0.3 relative to atmospheric pressure, a BETspecific surface area was measured by a nitrogen adsorption BETmultipoint method according to a flowing gas method.

Pore Volume

Using an Autoforb (Quantachrome Co.), a sample was placed in a powdercell, and the cell was sealed and pre-treated at 350° C. under vacuum(1.3 Pa or lower) for 2 hours, after which an adsorption isotherm(adsorption gas: nitrogen) was measured at liquid nitrogen temperature.Using the adsorption isotherm obtained, a BJH analysis was performed todetermine a micropore distribution, from which the cumulative porevolume at pore diameters in a range of 2 to 4 nm, the cumulative porevolume at pore diameters in a range of 2 to 100 nm, and the maximumdV/dlog (D) (V: cumulative pore volume, D: pore diameter) at porediameters in a range of 2 to 4 nm were calculated. The dV/dlog (D) wasmeasured such that the interval of log (D) was 0.010 to 0.050.

Example G1

A flake natural graphite having a d50 of 100 μm was crushed with amechanical crusher having a crushing rotor and a liner to give a flakenatural graphite having a d50 of 8.5 μm. To 100 g of the resulting flakenatural graphite, 12 g of a granulating agent of a paraffinic oil(liquid paraffin available from Wako Pure Chemical Industries, Ltd.,first grade, physical properties at 25° C.: viscosity=95 cP, contactangle=13.2°, surface tension=31.7 mN/m, r cos θ=30.9) was added andmixed with stirring. The sample obtained was disintegrated and mixedusing a hammer mill (MF10 available from IKA) at a rotation speed of3,000 rpm to give a flake natural graphite to which the granulatingagent uniformly adhered.

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., the flake natural graphite to which the granulating agentuniformly adhered was mechanically spheroidized at a rotor peripheralspeed of 85 m/sec for 10 minutes while fine powder generated during thespheroidization was deposited on the base material and incorporated intothe spheroidized particles, and heat treated in an inert gas at 720° C.to give a spheroidized natural graphite having a d50 of 12.9 μm. Usingthe measurement methods described above, d50, SA, Tap, pore volume,low-temperature output characteristics, and initial discharge capacitywere measured. The results are shown in Table 1G.

Example G2

A flake natural graphite having a d50 of 100 μm was crushed with amechanical crusher having a crushing rotor and a liner to give a flakenatural graphite having a d50 of 30 μm. To 100 g of the resulting flakenatural graphite, 4 g of a granulating agent of a paraffinic oil (liquidparaffin available from Wako Pure Chemical Industries, Ltd., firstgrade, physical properties at 25° C.: viscosity=95 cP, contactangle=13.2°, surface tension=31.7 mN/m, r cos θ=30.9) was added andmixed with stirring. The sample obtained was disintegrated and mixedusing a hammer mill (MF10 available from IKA) at a rotation speed of3,000 rpm to give a flake natural graphite to which the granulatingagent uniformly adhered. Using a Model NHS-1 hybridization systemavailable from Nara Machinery Co., Ltd., the flake natural graphite towhich the granulating agent uniformly adhered was mechanicallyspheroidized at a rotor peripheral speed of 85 m/sec for 10 minuteswhile fine powder generated during the spheroidization was deposited onthe base material and incorporated into the spheroidized particles, andheat treated in an inert gas at 720° C. to give a spheroidized naturalgraphite having a d50 of 16.3 μm. The results of the measurements madein the same manner as in Example G1 are shown in Table 1G.

Example G3

A flake natural graphite having a d50 of 100 μm was crushed with amechanical crusher having a crushing rotor and a liner to give a flakenatural graphite having a d50 of 30 μm. To 100 g of the resulting flakenatural graphite, 6 g of a granulating agent of a paraffinic oil (liquidparaffin available from Wako Pure Chemical Industries, Ltd., firstgrade, physical properties at 25° C.: viscosity=95 cP, contactangle=13.2°, surface tension=31.7 mN/m, r cos θ=30.9) was added andmixed with stirring. The sample obtained was disintegrated and mixedusing a hammer mill (MF10 available from IKA) at a rotation speed of3,000 rpm to give a flake natural graphite to which the granulatingagent uniformly adhered. Using a Model NHS-1 hybridization systemavailable from Nara Machinery Co., Ltd., the flake natural graphite towhich the granulating agent uniformly adhered was mechanicallyspheroidized at a rotor peripheral speed of 85 m/sec for 10 minuteswhile fine powder generated during the spheroidization was deposited onthe base material and incorporated into the spheroidized particles, andheat treated in an inert gas at 720° C. to give a spheroidized naturalgraphite having a d50 of 19.4 μm. The results of the measurements madein the same manner as in Example G1 are shown in Table 1G.

Comparative Example G1

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite and flake graphite fine powder generated duringthe spheroidization that were not deposited on the base material orincorporated. This sample was classified to remove the flake graphitefine powder, thereby providing a spheroidized graphite having a d50 of10.9 μm. The results of the measurements made in the same manner as inExample G1 are shown in Table 1G.

Comparative Example G2

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 5minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite and flake graphite fine powder generated duringthe spheroidization that were not deposited on the base material orincorporated. This sample was heat treated in an inert gas at 720° C.and classified to remove the flake graphite fine powder, therebyproviding a spheroidized graphite having a d50 of 15.7 μm. The resultsof the measurements made in the same manner as in Example G1 are shownin Table 1G.

Comparative Example G3

A flake natural graphite having a d50 of 100 μm was crushed with amechanical crusher having a crushing rotor and a liner to give a flakenatural graphite having a d50 of 9.8 μm. The results of the measurementsmade in the same manner as in Example G1 are shown in Table 1G.

TABLE 1G Pore Maximum Low-Temperature Volume at Pore Volume dV/dlog (D)Output Pore at Pore at Pore Characteristics, Initial Diameters DiametersDiameters of (Comparative Discharge d50 Tap SA of 2 to 4 of 2 to 100 2to 4 nm Example G1 = Capacity (μm) (g/cm³) (m²/g) nm (cm³/g) nm(cm^(3/)g) (cm³/g) 100) (mAh/g) Example G1 12.9 0.88 15.3 0.0037 0.05600.0143 130 361 Example G2 16.3 1.03 13.8 0.0038 0.0405 0.0163 111 362Example G3 19.4 1.06 13.4 0.0035 0.0487 0.0154 107 362 Comparative 10.90.88 8.4 0.0020 0.0234 0.0087 100 369 Example G1 Comparative 15.7 1.026.9 0.0018 0.0156 0.0079 89 368 Example G2 Comparative 9.8 0.69 7.10.0023 0.0223 0.0103 100 369 Example G3

The carbon materials of Examples G1 to G3 provided excellentlow-temperature output characteristics. This is probably because ofabundant lithium-ion insertion/extraction sites due to a largecumulative pore volume at pore diameters in a range of 2 to 4 nm, andthe smooth movement of electrolyte solution between particles due to ahigh tap density.

Eighth examples (Examples H) of the present invention will now bedescribed.

In Examples H, physical properties of negative electrode materialsproduced were measured by the following methods.

Preparation of Electrode Sheet

An electrode plate having an active material layer with an activematerial layer density of 1.60±0.03 g/cm³ was prepared using graphiteparticles of Examples or Comparative Examples. Specifically, 50.00±0.02g of a negative electrode material, 50.00±0.02 g (0.500 g on a solidsbasis) of a 1% by mass aqueous carboxymethylcellulose sodium saltsolution, and 1.00±0.05 g (0.5 g on a solids basis) of an aqueousdispersion of a styrene-butadiene rubber having a weight averagemolecular weight of 270,000 were stirred with a Keyence hybrid mixer for5 minutes, and the mixture was defoamed for 30 seconds to give a slurry.

The slurry was applied to a 10-μm-thick copper foil, serving as acurrent collector, to a width of 10 cm using a small die coateravailable from Itochu Machining Co., Ltd. such that the negativeelectrode material adhered in an amount of 6.0±0.3 mg/cm² or 9.0±0.3mg/cm². The coated foil was roll-pressed using a roller having adiameter of 20 cm to adjust the density of the active material layer tobe 1.35±0.03 g/cm³ or 1.60±0.03 g/cm³, thereby preparing an electrodesheet.

Production of Non-Aqueous Secondary Battery (2016 Coin Battery)

The electrode sheet prepared by the above-described method, to which thenegative electrode material adhered in an amount of 9.0±0.3 mg/cm² andin which the density of the active material layer was 1.60±0.03 g/cm³,was cut into a disk having a diameter of 12.5 mm, and lithium metal foilwas cut into a disk having a diameter of 14 mm to prepare a counterelectrode. A separator (made of a porous polyethylene film) was placedbetween the two electrodes, the separator being impregnated with anelectrolyte solution of 1 mol/L of LiPF₆ in a mixed solvent of ethylenecarbonate and ethyl methyl carbonate (volume ratio=3:7). In this manner,2016 coin batteries were produced.

Method of Producing Non-Aqueous Secondary Battery (Laminate Battery)

The electrode sheet prepared by the above-described method, to which thenegative electrode material adhered in an amount of 6.0±0.3 mg/cm² andin which the density of the active material layer was 1.35±0.03 g/cm³,was cut to 4 cm×3 cm to prepare a negative electrode, and a positiveelectrode made of NMC was cut to the same area. The negative electrodeand the positive electrode were combined with a separator (made of aporous polyethylene film) placed therebetween. An electrolyte solutionof 1.2 mol/L of LiPF₆ in a mixed solvent of ethylene carbonate, ethylmethyl carbonate, and dimethyl carbonate (volume ratio=3:3:4) wasinjected in an amount of 200 μL to produce a laminate battery.

Method for Measuring Discharge Capacity

Using the non-aqueous secondary battery (2016 coin battery) produced bythe above-described method, the capacity of the battery during chargingand discharging was measured by the following method.

The lithium counter electrode was charged to 5 mV at a current densityof 0.05 C and further charged at a constant voltage of 5 mV to a currentdensity of 0.005 C. The negative electrode was doped with lithium, andthen the lithium counter electrode was discharged to 1.5 V at a currentdensity of 0.1 C. Subsequently, a second charging and discharging wasperformed at the same current density. The discharge capacity at thesecond cycle was defined as a discharge capacity of this battery.

Low-Temperature Output Characteristics

Using the laminate non-aqueous electrolyte secondary battery produced bythe method for producing a non-aqueous electrolyte secondary batterydescribed above, low-temperature output characteristics were measured bythe following method.

A non-aqueous electrolyte secondary battery that had yet to go through acharge and discharge cycle was subjected to an initial charge anddischarge that involves three cycles in a voltage range of 4.1 V to 3.0V at 25° C. and a current of 0.2 C (1 C is a current at which a ratedcapacity at a 1-hour rate discharge capacity is discharged in 1 hour,and so on) and two cycles in a voltage range of 4.2 V to 3.0 V at acurrent of 0.2 C (in charging, a constant-voltage charge at 4.2 V wasfurther performed for 2.5 hours).

Furthermore, charging was performed at a current of 0.2 C to an SOC of50%, and then constant-current discharging was performed in alow-temperature environment at −30° C. for 2 seconds at varying currentsof ⅛ C, ¼ C, ½ C, 1.5 C, and 2 C. The battery voltage drop at 2 secondsafter discharging under each condition was measured. From eachmeasurement, a current I that could be passed in 2 seconds when theupper limit charge voltage was 3 V was calculated, and a valuecalculated from the formula: 3×I (W) was defined as the low-temperatureoutput characteristics of each battery.

Measurement of Thermal Weight Loss (□TG) (%)

Into a platinum pan, 5 mg of a carbon material was weighed, and the panwas placed in a differential thermal balance (TG8120 available fromRigaku Corporation). Under an air stream of 100 mL/min, the temperaturewas raised from room temperature to 400° C. at a rate of 20° C./min andthen from 400° C. to 600° C. at a rate of 2° C./min, and the amount ofthermal weight loss was measured. The thermal weight loss between 400°C. and 600° C. in this measurement was calculated and defined as athermal weight loss (□TG) (%) in the present invention.

BET Specific Surface Area (SA)

Using a surface area meter (AMS8000 specific surface area analyzeravailable from Ohkura Riken Co., Ltd.), 0.4 g of a carbon material wasloaded into a cell, and the carbon material sample was preliminarilydried under a nitrogen stream at 350° C. for 15 minutes, after whichusing a nitrogen-helium mixed gas precisely regulated so as to have anitrogen pressure of 0.3 relative to atmospheric pressure, a BETspecific surface area was measured by a nitrogen adsorption BET methodaccording to a flowing gas method.

Raman R Value

The measurement was made as follows: using a Raman spectroscope (Ramanspectroscope available from JASCO Corporation), a sample was loaded bygravity-dropping a carbon material into a measuring cell, and themeasuring cell was irradiated with an argon-ion laser beam while beingrotated in a plane perpendicular to the laser beam.

Wavelength of argon-ion laser beam: 514.5 nm

Laser power on sample: 25 mW

Resolution: 4 cm⁻¹

Measurement range: 1,100 cm⁻¹ to 1,730 cm⁻¹.

Measurement of peak intensity, measurement of peak half-width:background processing, smoothing processing (convolution by simpleaverage, 5 points)

d50

The d50 was determined as a volume-based median diameter by suspending0.01 g of a carbon material in 10 mL of a 0.2% by mass aqueous solutionof a polyoxyethylene sorbitan monolaurate surfactant (Tween 20(registered trademark)), placing the suspension (a measurement sample)in a commercially available laser diffraction/scattering particle sizedistribution analyzer (e.g., LA-920 available from HORIBA, Ltd.),irradiating the measurement sample with ultrasonic waves of 28 kHz at apower of 60 W for 1 minute, and then performing a measurement with theanalyzer.

Roundness

Using a flow-type particle image analyzer (FPIA-2000 available fromSysmex Corporation), a particle size distribution based on equivalentcircle diameter was measured, and a roundness was determined.Ion-exchanged water was used as a dispersion medium, and polyoxyethylene(20) monolaurate was used as a surfactant. The equivalent circlediameter is a diameter of a circle (equivalent circle) having the sameprojected area as that of a captured particle image, and the roundnessis a ratio of the perimeter of the equivalent circle, as the numerator,to the perimeter of the captured particle projection image, as thedenominator. Roundnesses of particles having an equivalent diameter inthe range of 1.5 to 40 μm were averaged to determine the roundness.

Tap Density

Using a powder density meter, the carbon material of the presentinvention was dropped through a sieve with openings of 300 μm into acylindrical tap cell with a diameter of 1.6 cm and a volume capacity of20 cm³ to fill up the cell, and then a tap with a stroke length of 10 mmwas given 1,000 times. The density calculated from the volume at thistime and the mass of the sample was defined as the tap density.

Example H1

A flake natural graphite having a d50 of 100 μm was crushed with a dryswirl-flow crusher to give a flake natural graphite having a d50 of 8.1μm and a Tap of 0.39 g/cm³. To 100 g of the resulting flake naturalgraphite, 12 g of a granulating agent of a liquid paraffin (Wako PureChemical Industries, Ltd., first grade, physical properties at 25° C.:viscosity=95 cP, contact angle=13.2°, surface tension=31.7 mN/m, r cosθ=30.9) was added and mixed with stirring. The sample obtained wasdisintegrated and mixed using a hammer mill (MF10 available from IKA) ata rotation speed of 3,000 rpm to give a flake natural graphite to whichthe granulating agent adhered. Using a Model NHS-1 hybridization systemavailable from Nara Machinery Co., Ltd., the sample obtained wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes. The sample obtained was heat treated in a nitrogen atmosphereat 500° C. to give a spheroidized graphite sample from which thegranulating agent was removed. Using the measurement methods describedabove, d50, SA, Tap, roundness, □TG (%)/SA (m²/g), Raman R value,discharge capacity, and low-temperature output characteristics weremeasured. The results are shown in Tables 1H and 2H.

Example H2

A sample was prepared in the same manner as in Example H1 except thatthe heat-treatment temperature was 700° C. The results of themeasurements made in the same manner as in Example H1 are shown inTables 1H and 2H.

Example H3

A sample was prepared in the same manner as in Example H1 except thatthe heat-treatment temperature was 850° C. The results of themeasurements made in the same manner as in Example H1 are shown inTables 1H and 2H.

Example H4

A sample was prepared in the same manner as in Example H1 except thatthe heat-treatment temperature was 1,000° C. The results of themeasurements made in the same manner as in Example H1 are shown inTables 1H and 2H.

Comparative Example H1

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite fine powder not deposited on the base materialor incorporated into the spheroidized particles. This sample wasclassified to remove the flake graphite fine powder, thereby providing aspheroidized graphite having a d50 of 10.8 μm. The results of themeasurements made in the same manner as in Example H1 are shown inTables 1H and 2H.

Comparative Example H2

A sample was prepared in the same manner as in Example H1 except thatthe spheroidized graphite of Comparative Example H1 was heat treated ina nitrogen atmosphere at 700° C. The results of the measurements made inthe same manner as in Example H1 are shown in Tables 1H and 2H.

Comparative Example H3

A sample was prepared in the same manner as in Comparative Example H2except that the heat-treatment temperature was 850° C. The results ofthe measurements made in the same manner as in Example H1 are shown inTables 1H and 2H.

Comparative Example H4

A sample was prepared in the same manner as in Comparative Example H2except that the heat-treatment temperature was 1,000° C. The results ofthe measurements made in the same manner as in Example H1 are shown inTables 1H and 2H.

Comparative Example H5

A sample was prepared in the same manner as in Comparative Example H2except that the heat-treatment temperature was 1,300° C. The results ofthe measurements made in the same manner as in Example H1 are shown inTables 1H and 2H.

Comparative Example H6

The spheroidized graphite of Comparative Example H1 and a coal-tarpitch, serving as an amorphous carbon precursor, were mixed and heattreated in an inert gas at 1,300° C., and then the burned product wasdisintegrated and classified to give a multi-layered carbon materialmade of graphite particles and an amorphous carbon combined with eachother. The burning yield showed that the mass ratio of spheroidizedgraphite particle to amorphous carbon (spheroidized graphiteparticle/amorphous carbon) of the multi-layered carbon material was1:0.07. The results of the measurements made in the same manner as inExample H1 are shown in Tables 1H and 2H.

Comparative Example H7

A sample was prepared in the same manner as in Example H1 except thatthe heat-treatment temperature was 1,300° C. The results of themeasurements made in the same manner as in Example H1 are shown inTables 1H and 2H.

Example H5

A flake natural graphite having a d50 of 100 μm was crushed with amechanical crusher having a crushing rotor and a liner to give a flakenatural graphite having a d50 of 30 μm. To 100 g of the resulting flakenatural graphite, 4 g of a granulating agent of a liquid paraffin (WakoPure Chemical Industries, Ltd., first grade, physical properties at 25°C.: viscosity=95 cP, contact angle=13.2°, surface tension=31.7 mN/m, rcos θ=30.9) was added and mixed with stirring. The sample obtained wasdisintegrated and mixed using a hammer mill (MF10 available from IKA) ata rotation speed of 3,000 rpm to give a flake natural graphite to whichthe granulating agent adhered. Using a Model NHS-1 hybridization systemavailable from Nara Machinery Co., Ltd., the sample obtained wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes. The sample obtained was heat treated in a nitrogen atmosphereat 700° C. to give a spheroidized graphite sample from which thegranulating agent was removed. The results of the measurements made inthe same manner as in Example H1 are shown in Tables 1H and 2H.

Comparative Example H8

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite fine powder not deposited on the base materialor incorporated into the spheroidized particles. This sample wasclassified to remove the flake graphite fine powder, thereby providing aspheroidized graphite having a d50 of 15.4 μm. The results of themeasurements made in the same manner as in Example H1 are shown inTables 1H and 2H.

Example H6

A sample was prepared in the same manner as in Example H4 except that 6g of a granulating agent of a liquid paraffin (Wako Pure ChemicalIndustries, Ltd., first grade) was added. The results of themeasurements made in the same manner as in Example H1 are shown inTables 1H and 2H.

Comparative Example H9

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 70 m/sec for 5minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite fine powder not deposited on the base materialor incorporated into the spheroidized particles. This sample wasclassified to remove the flake graphite fine powder, thereby providing aspheroidized graphite having a d50 of 18.2 μm. The results of themeasurements made in the same manner as in Example H1 are shown inTables 1H and 2H.

TABLE 1H ΔTG d50 SA, Tap, (%)/SA Raman R (X) μm m²/g g/cm³ Roundness(m²/g) value Example H1 12.2 15.9 0.84 0.94 0.29 0.38 Example H2 12.915.3 0.88 0.94 0.20 0.38 Example H3 12.4 16.0 0.93 0.94 0.14 0.38Example H4 12.3 15.9 0.94 0.94 0.12 0.37 Comparative 10.8 7.2 0.87 0.920.35 0.24 Example H1 Comparative 10.9 7.3 0.92 0.92 0.51 0.32 Example H2Comparative 11.1 7.4 0.95 0.92 0.21 0.29 Example H3 Comparative 11.2 7.40.96 0.92 0.12 0.29 Example H4 Comparative 10.8 7.1 0.98 0.92 0.02 0.15Example H5 Comparative 11.4 2.8 1.04 0.92 0.47 0.37 Example H6Comparative 12.6 15.5 0.97 0.94 0.03 0.16 Example H7 Example H5 16.313.8 1.03 0.93 0.15 0.39 Comparative 15.4 5.9 1.01 0.93 0.35 0.24Example H8 Example H6 19.4 13.4 1.06 0.93 0.14 0.35 Comparative 18.2 5.61.08 0.93 0.31 0.27 Example H9

TABLE 2H Low-Temperature Output Characteristics, Discharge (ComparativeCapacity, Example H1 = mAh/g 100) Example H1 365 122 Example H2 367 126Example H3 364 118 Example H4 364 118 Comparative 365 100 Example H1Comparative 363 86 Example H2 Comparative 366 88 Example H3 Comparative366 94 Example H4 Comparative 366 89 Example H5 Comparative 358 103Example H6 Comparative 365 114 Example H7 Example H5 368 116 Comparative367 91 Example H8 Example H6 367 117 Comparative 367 89 Example H9

In Examples H1 to H6, the flake natural graphite adjusted to have aprescribed particle size was granulated with a granulating agent havingprescribed physical properties added, whereby a Raman R value and a□TG/SA value in the prescribed ranges were successfully achieved toprovide a high capacity and excellent low-temperature outputcharacteristics. By contrast, in Comparative Examples H1 to H9, wherethe Raman R value and/or the □TG/SA value were outside the prescribedranges, degraded low-temperature output characteristics were provided.

Ninth examples (Examples I) of the present invention will now bedescribed.

In the Examples, physical properties of negative electrode materialsproduced were measured by the following methods. The viscosity, contactangle, surface tension, and r cos θ of granulating agents were eachmeasured by the methods described in the specification.

Preparation of Electrode Sheet

An electrode plate having an active material layer with an activematerial layer density of 1.35±0.03 g/cm³ or 1.60±0.03 g/cm³ wasprepared using graphite particles of Examples or Comparative Examples.Specifically, 50.00±0.02 g of a negative electrode material, 50.00±0.02g (0.500 g on a solids basis) of a 1% by mass aqueouscarboxymethylcellulose sodium salt solution, and 1.00±0.05 g (0.5 g on asolids basis) of an aqueous dispersion of a styrene-butadiene rubberhaving a weight average molecular weight of 270,000 were stirred with aKeyence hybrid mixer for 5 minutes, and the mixture was defoamed for 30seconds to give a slurry.

The slurry was applied to a 10-μm-thick copper foil, serving as acurrent collector, to a width of 10 cm using a small die coateravailable from Itochu Machining Co., Ltd. such that the negativeelectrode material adhered in an amount of 6.0±0.3 mg/cm² or 9.0±0.3mg/cm². The coated foil was roll-pressed using a roller having adiameter of 20 cm to adjust the density of the active material layer tobe 1.35±0.03 g/cm³ or 1.60±0.03 g/cm³, thereby preparing an electrodesheet.

Production of Non-Aqueous Secondary Battery (2016 Coin Battery)

The electrode sheet prepared by the above-described method, to which thenegative electrode material adhered in an amount of 9.0±0.3 mg/cm² andin which the density of the active material layer was 1.60±0.03 g/cm³,was cut into a disk having a diameter of 12.5 mm, and lithium metal foilwas cut into a disk having a diameter of 14 mm to prepare a counterelectrode. A separator (made of a porous polyethylene film) was placedbetween the two electrodes, the separator being impregnated with anelectrolyte solution of 1 mol/L of LiPF₆ in a mixed solvent of ethylenecarbonate and ethyl methyl carbonate (volume ratio=3:7). In this manner,2016 coin batteries were produced.

Method of Producing Non-Aqueous Secondary Battery (Laminate Battery)

The electrode sheet prepared by the above-described method, to which thenegative electrode material adhered in an amount of 6.0±0.3 mg/cm² andin which the density of the active material layer was 1.35±0.03 g/cm²,was cut to 4 cm×3 cm to prepare a negative electrode, and a positiveelectrode made of NMC was cut to the same area. The negative electrodeand the positive electrode were combined with a separator (made of aporous polyethylene film) placed therebetween. An electrolyte solutionof 1.2 mol/L of LiPF₆ in a mixed solvent of ethylene carbonate, ethylmethyl carbonate, and dimethyl carbonate (volume ratio=3:3:4) wasinjected in an amount of 200 μl to produce a laminate battery.

Method for Measuring Discharge Capacity

Using the non-aqueous secondary battery (2016 coin battery) produced bythe above-described method, the capacity of the battery during chargingand discharging was measured by the following method.

The lithium counter electrode was charged to 5 mV at a current densityof 0.05 C and further charged at a constant voltage of 5 mV to a currentdensity of 0.005 C. The negative electrode was doped with lithium, andthen the lithium counter electrode was discharged to 1.5 V at a currentdensity of 0.1 C. Subsequently, a second charging and discharging wasperformed at the same current density. The discharge capacity at thesecond cycle was defined as a discharge capacity of this battery.

Low-Temperature Output Characteristics

Using the laminate non-aqueous electrolyte secondary battery produced bythe method for producing a non-aqueous electrolyte secondary batterydescribed above, low-temperature output characteristics were measured bythe following method.

A non-aqueous electrolyte secondary battery that had yet to go through acharge and discharge cycle was subjected to an initial charge anddischarge that involves three cycles in a voltage range of 4.1 V to 3.0V at 25° C. and a current of 0.2 C (1 C is a current at which a ratedcapacity at a 1-hour rate discharge capacity is discharged in 1 hour,and so on) and two cycles in a voltage range of 4.2 V to 3.0 V at acurrent of 0.2 C (in charging, a constant-voltage charge at 4.2 V wasfurther performed for 2.5 hours).

Furthermore, charging was performed at a current of 0.2 C to an SOC of50%, and then constant-current discharging was performed in alow-temperature environment at −30° C. for 2 seconds at varying currentsof ⅛ C, ¼ C, ½ C, 1.5 C, and 2 C. The battery voltage drop at 2 secondsafter discharging under each condition was measured. From eachmeasurement, a current I that could be passed in 2 seconds when theupper limit charge voltage was 3 V was calculated, and a valuecalculated from the formula: 3×I (W) was defined as the low-temperatureoutput characteristics of each battery.

Surface Oxygen Content (O/C) For X-ray photoelectron spectroscopy, anX-ray photoelectron spectroscope was used. A measuring object wasmounted on a sample stage such that the surface of the object was flat,and a multiplex measurement was performed using a Kα radiation ofaluminum as an X-ray source to measure spectra of C1s (280 to 300 eV)and 01s (525 to 545 eV).

Charge correction was performed with the C1s peak top obtained set to284.3 eV. Peak areas of the spectra of C1s and O1s were determined andthen multiplied by an apparatus sensitivity to determine the surfaceatom concentrations of C and O. The O/C ratio of the atom concentrationsof O and C obtained (O atom concentration/C atom concentration)×100 wasdefined as the surface oxygen content O/C value of the carbon material.

Total Oxygen Content

An oxygen/nitrogen/hydrogen analyzer (TCH600 ONH determinator availablefrom LECO) was used. In an inert gas atmosphere impulse furnace, 50 mgof the carbon material was melted and decomposed, and the amounts ofcarbon monoxide and carbon dioxide in a discharged carrier gas weremeasured using an infrared detector to determine the total oxygencontent (mol %) of the carbon material.

BET Specific Surface Area (SA)

Using a surface area meter (AMS8000 specific surface area analyzeravailable from Ohkura Riken Co., Ltd.), 0.4 g of a carbon material wasloaded into a cell, and the carbon material sample was preliminarilydried under a nitrogen stream at 350° C. for 15 minutes, after whichusing a nitrogen-helium mixed gas precisely regulated so as to have anitrogen pressure of 0.3 relative to atmospheric pressure, a BETspecific surface area was measured by a nitrogen adsorption BET methodaccording to a flowing gas method.

d50

The d50 was determined as a volume-based median diameter by suspending0.01 g of a carbon material in 10 mL of a 0.2% by mass aqueous solutionof a polyoxyethylene sorbitan monolaurate surfactant (Tween 20(registered trademark)), placing the suspension (a measurement sample)in a commercially available laser diffraction/scattering particle sizedistribution analyzer (e.g., LA-920 available from HORIBA, Ltd.),irradiating the measurement sample with ultrasonic waves of 28 kHz at apower of 60 W for 1 minute, and then performing a measurement with theanalyzer.

Roundness (Average Roundness)

Using a flow-type particle image analyzer (FPIA-2000 available fromSysmex Corporation), a particle size distribution based on equivalentcircle diameter was measured, and a roundness was determined.Ion-exchanged water was used as a dispersion medium, and polyoxyethylene(20) monolaurate was used as a surfactant. The equivalent circlediameter is a diameter of a circle (equivalent circle) having the sameprojected area as that of a captured particle image, and the roundnessis a ratio of the perimeter of the equivalent circle, as the numerator,to the perimeter of the captured particle projection image, as thedenominator. Roundnesses of particles having an equivalent diameter inthe range of 1.5 to 40 μm were averaged to determine the roundness.

Tap Density

Using a powder density meter, the carbon material of the presentinvention was dropped through a sieve with openings of 300 μm into acylindrical tap cell with a diameter of 1.6 cm and a volume capacity of20 cm³ to fill up the cell, and then a tap with a stroke length of 10 mmwas given 1,000 times. The density calculated from the volume at thistime and the mass of the sample was defined as the tap density.

Oxygen Functional Group Dispersity

The oxygen functional group dispersity was determined by the followingformula.

Oxygen functional group dispersity (Y _(i))=total oxygen content (mol %)determined by elemental analysis/surface oxygen content (O/C) (mol %)determined by X-ray photoelectron spectroscopy

Example I1

A flake natural graphite having a d50 of 100 μm was crushed with a dryswirl-flow crusher to give a flake natural graphite having a d50 of 8.1μm, a Tap of 0.39 g/cm³, and a water content of 0.08% by mass. To 100 gof the resulting flake natural graphite, 12 g of a granulating agent ofa liquid paraffin (Wako Pure Chemical Industries, Ltd., first grade,physical properties at 25° C.: viscosity=95 cP, contact angle=13.2°,surface tension=31.7 mN/m, r cos θ=30.9) was added and mixed withstirring. The sample obtained was disintegrated and mixed using a hammermill (MF10 available from IKA) at a rotation speed of 3,000 rpm to givea flake natural graphite to which the granulating agent adhered. Using aModel NHS-1 hybridization system available from Nara Machinery Co.,Ltd., the sample obtained was mechanically granulated at a rotorperipheral speed of 85 m/sec for 10 minutes. The sample obtained washeat treated in a nitrogen atmosphere at 500° C. to give a granulatedcarbon material from which the granulating agent was removed. Using themeasurement methods described above, d50, SA, Tap, roundness, O/C, totaloxygen content, oxygen functional group dispersity, discharge capacity,and low-temperature output characteristics were measured. The resultsare shown in Tables 1I and 2I.

Example I2

A sample was prepared in the same manner as in Example I1 except thatthe heat-treatment temperature was 700° C. The results of themeasurements made in the same manner as in Example I1 are shown inTables 1I and 2I.

Example I3

A flake natural graphite having a d50 of 100 μm was crushed with amechanical crusher having a crushing rotor and a liner to give a flakenatural graphite having a d50 of 30 μm and a water content of 0.03% bymass. To 100 g of the resulting flake natural graphite, 4 g of agranulating agent of a liquid paraffin (Wako Pure Chemical Industries,Ltd., first grade, physical properties at 25° C.: viscosity=95 cP,contact angle=13.2°, surface tension=31.7 mN/m, r cos θ=30.9) was addedand mixed with stirring. The sample obtained was disintegrated and mixedusing a hammer mill (MF10 available from IKA) at a rotation speed of3,000 rpm to give a flake natural graphite to which the granulatingagent adhered. Using a Model NHS-1 hybridization system available fromNara Machinery Co., Ltd., the sample obtained was mechanicallygranulated at a rotor peripheral speed of 85 m/sec for 10 minutes. Thesample obtained was heat treated in a nitrogen atmosphere at 700° C. togive a granulated carbon material from which the granulating agent wasremoved. The results of the measurements made in the same manner as inExample I1 are shown in Tables 1I and 2I.

Example I4

A sample was prepared in the same manner as in Example I3 except that 6g of a granulating agent of a liquid paraffin (Wako Pure ChemicalIndustries, Ltd., first grade) was added. The results of themeasurements made in the same manner as in Example I1 are shown inTables 1I and 2I.

Comparative Example I1

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically granulated at a rotor peripheral speed of 85 m/sec for 10minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite fine powder not deposited on the base materialor incorporated into the granulated particles. This sample wasclassified to remove the flake graphite fine powder, thereby providing agranulated carbon material having a d50 of 10.9 μm. The results of themeasurements made in the same manner as in Example I1 are shown inTables 1I and 2I.

Comparative Example I2

A sample was prepared in the same manner as in Example 1 except that thegranulated carbon material of Comparative Example I1 was heat treated ina nitrogen atmosphere at 700° C. The results of the measurements made inthe same manner as in Example I1 are shown in Tables 1I and 2I.

Comparative Example I3

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically granulated at a rotor peripheral speed of 85 m/sec for 5minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite fine powder not deposited on the base materialor incorporated into the granulated particles. This sample wasclassified to remove the flake graphite fine powder, thereby providing agranulated carbon material having a d50 of 15.4 μm. The results of themeasurements made in the same manner as in Example I1 are shown inTables 1I and 2I.

Comparative Example I4

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically granulated at a rotor peripheral speed of 70 m/sec for 3minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite fine powder not deposited on the base materialor incorporated into the granulated particles. This sample wasclassified to remove the flake graphite fine powder, thereby providing agranulated carbon material having a d50 of 19.5 μm. The granulatedcarbon material was further mechanically granulated at a rotorperipheral speed of 70 m/sec for 3 minutes using a Model NHS-1hybridization system available from Nara Machinery Co., Ltd. and thenclassified to remove the flake graphite fine powder not deposited on thebase material or incorporated into the granulated particles, therebyproviding a granulated carbon material having a d50 of 18.2 μm. Theresults of the measurements made in the same manner as in Example I1 areshown in Tables 1I and 2I.

TABLE 1I Oxy- To- gen tal Func- Oxy- tional gen Group O/ Con- Dis- d50Tap, C, tent, per- 100Y_(i) (X_(i)), g/ SA, mol mol sity + Round- μm cm³m²/g % % (Y_(i)) 0.26X_(i) ness Example 12.7 0.87 15.4 0.72 0.078 0.10814.1 0.94 I1 Example 12.9 0.88 15.3 0.78 0.055 0.071 10.4 0.94 I2Example 16.3 1.03 13.8 0.65 0.041 0.063 10.5 0.93 I3 Example 19.4 1.0613.4 0.72 0.034 0.047 9.7 0.93 I4 Com- 10.9 0.88 8.4 2.79 0.183 0.0669.4 0.92 parative Example I1 Com- 11.3 0.89 8.4 0.83 0.050 0.060 9.00.92 parative Example I2 Com- 15.4 1.01 5.9 2.60 0.139 0.053 9.3 0.93parative Example I3 Com- 18.2 1.08 5.6 2.31 0.109 0.047 9.4 0.93parative Example I4

TABLE 2I Low-Temperature Output Characteristics, Discharge (ComparativeCapacity, Example I1 = mAh/g 100) Example I1 365 122 Example I2 367 126Example I3 368 116 Example I4 367 117 Comparative 365 100 Example I1Comparative 363 86 Example I2 Comparative 367 91 Example I3 Comparative367 89 Example I4

In Examples I1 to 14, the flake natural graphite adjusted to have aprescribed particle size was granulated with a granulating agent havingprescribed physical properties added, whereby the relationship betweenoxygen functional group dispersity and d50 (μm) in the prescribed rangewas successfully achieved to provide a high capacity and excellentlow-temperature output characteristics. By contrast, in ComparativeExamples I1 to I4, where the relationship between oxygen functionalgroup dispersity and d50 (μm) was outside the prescribed range, degradedlow-temperature output characteristics were provided.

Tenth examples (Examples J) of the present invention will now bedescribed.

In Examples J, physical properties and characteristics of carbonmaterials produced were measured by the following methods.

d50

The d50 was determined as a volume-based median diameter by suspending0.01 g of a negative electrode material in 10 mL of a 0.2% by massaqueous solution of a polyoxyethylene sorbitan monolaurate surfactant(Tween 20 (registered trademark)), placing the suspension (a measurementsample) in a commercially available laser diffraction/scatteringparticle size distribution analyzer (e.g., LA-920 available from HORIBA,Ltd.), irradiating the measurement sample with ultrasonic waves of 28kHz at a power of 60 W for 1 minute, and then performing a measurementwith the analyzer.

Tap Density

Using a powder density meter, the negative electrode material wasdropped through a sieve with openings of 300 μm into a cylindrical tapcell with a diameter of 1.6 cm and a volume capacity of 20 cm³ to fillup the cell, and then a tap with a stroke length of 10 mm was given1,000 times. The density calculated from the volume at this time and themass of the sample was defined as the tap density.

Specific Surface Area SA

The specific surface area SA was defined as a value determined asfollows: using a surface area meter (Gemini 2360 specific surface areaanalyzer available from Shimadzu Corporation), a negative electrodematerial sample was preliminarily vacuum dried under a nitrogen streamat 100° C. for 3 hours and then cooled to liquid nitrogen temperature,and using a nitrogen-helium mixed gas precisely regulated so as to havea nitrogen pressure of 0.3 relative to atmospheric pressure, a BETspecific surface area was measured by a nitrogen adsorption BETmultipoint method according to a flowing gas method.

Preparation of Electrode Sheet

An electrode plate having an active material layer with an activematerial layer density of 1.60±0.03 g/cm³ or 1.35±0.03 g/cm³ wasprepared using a negative electrode material of Examples or ComparativeExamples. Specifically, 50.00±0.02 g of a negative electrode material,50.00±0.02 g (0.500 g on a solids basis) of a 1% by mass aqueouscarboxymethylcellulose sodium salt solution, and 1.00±0.05 g (0.5 g on asolids basis) of an aqueous dispersion of a styrene-butadiene rubberhaving a weight average molecular weight of 270,000 were stirred with aKeyence hybrid mixer for 5 minutes, and the mixture was defoamed for 30seconds to give a slurry.

The slurry was applied to a 10-μm-thick copper foil, serving as acurrent collector, to a width of 10 cm using a small die coateravailable from Itochu Machining Co., Ltd. such that the negativeelectrode material adhered in an amount of 12.00±0.3 mg/cm² or 6.00±0.3mg/cm². The coated foil was roll-pressed using a roller having adiameter of 20 cm to adjust the density of the active material layer tobe 1.60±0.03 g/cm³ or 1.35±0.03 g/cm³, thereby preparing an electrodesheet.

Production of Non-Aqueous Secondary Battery (2016 Coin Battery)

The electrode sheet prepared by the above-described method, to which thenegative electrode material adhered in an amount of 12.00±0.3 mg/cm² andin which the density of the active material layer was adjusted to be1.60±0.03 g/cm³, was cut into a disk having a diameter of 12.5 mm, andlithium metal foil was cut into a disk having a diameter of 14 mm toprepare a counter electrode. A separator (made of a porous polyethylenefilm) was placed between the two electrodes, the separator beingimpregnated with an electrolyte solution of 1 mol/L of LiPF₆ in a mixedsolvent of ethylene carbonate and ethyl methyl carbonate (volumeratio=3:7). In this manner, 2016 coin batteries were produced.

Method of Producing Non-Aqueous Secondary Battery (Laminate Battery)

The electrode sheet prepared by the above-described method, to which thenegative electrode material adhered in an amount of 6.00±0.3 mg/cm² andin which the density of the active material layer was adjusted to be1.35±0.03 g/cm³, was cut to 4 cm×3 cm to prepare a negative electrode,and a positive electrode made of NMC was cut to the same area. Thenegative electrode and the positive electrode were combined with aseparator (made of a porous polyethylene film) placed therebetween. Anelectrolyte solution of 1.2 mol/L of LiPF₆ in a mixed solvent ofethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate(volume ratio=3:3:4) was injected in an amount of 200 μL to produce alaminate battery.

Method for Measuring Discharge Capacity

Using the non-aqueous secondary battery (2016 coin battery) produced bythe above-described method, the capacity of the battery during chargingand discharging was measured by the following method.

The lithium counter electrode was charged to 5 mV at a current densityof 0.05 C and further charged at a constant voltage of 5 mV to a currentdensity of 0.005 C. The negative electrode was doped with lithium, andthen the lithium counter electrode was discharged to 1.5 V at a currentdensity of 0.1 C. The discharge capacity at this time was defined as adischarge capacity of this battery.

Low-Temperature Output Characteristics

Using the laminate non-aqueous electrolyte secondary battery produced bythe method for producing a non-aqueous electrolyte secondary batterydescribed above, low-temperature output characteristics were measured bythe following method.

A non-aqueous electrolyte secondary battery that had yet to go through acharge and discharge cycle was subjected to an initial charge anddischarge that involves three cycles in a voltage range of 4.1 V to 3.0V at 25° C. and a current of 0.2 C (1 C is a current at which a ratedcapacity at a 1-hour rate discharge capacity is discharged in 1 hour,and so on) and two cycles in a voltage range of 4.2 V to 3.0 V at acurrent of 0.2 C (in charging, a constant-voltage charge at 4.2 V wasfurther performed for 2.5 hours).

Furthermore, charging was performed at a current of 0.2 C to an SOC of50%, and then constant-current discharging was performed in alow-temperature environment at −30° C. for 2 seconds at varying currentsof ⅛ C, ¼ C, ½ C, 1.5 C, and 2 C. The battery voltage drop at 2 secondsafter discharging under each condition was measured. From eachmeasurement, a current I that could be passed in 2 seconds when theupper limit charge voltage was 3 V was calculated, and a valuecalculated from the formula: 3×I (W) was defined as the low-temperatureoutput characteristics of each battery.

High-Temperature Storage Characteristics

High-temperature storage characteristics were measured by the followingmeasurement method using the laminate non-aqueous electrolyte secondarybattery produced by the method for producing a non-aqueous electrolytesecondary battery described above.

A non-aqueous electrolyte secondary battery that has yet to go through acharge and discharge cycle was subjected to an initial charge anddischarge that involves three cycles in a voltage range of 4.1 V to 3.0V at 25° C. and a current of 0.2 C (1 C is a current at which a ratedcapacity at a 1-hour rate discharge capacity is discharged in 1 hour,and so on) and two cycles in a voltage range of 4.2 V to 3.0 V at acurrent of 0.2 C (in charging, a constant-voltage charge at 4.2 V wasfurther performed for 2.5 hours).

The battery was further charged at a current of 0.2 C to an SOC of 80%and then stored in a high-temperature environment at 60° C. for 2 weeks.After that, the battery was discharged at 25° C. and 0.2 C to 3.0 V,charged at 0.2 C to 4.2 V, and discharged at 0.2 C to 3.0 V. Thedischarge capacity at this time was defined as a discharge capacity A(mAh). The ratio (%) of the discharge capacity A to a discharge capacityB (mAh) at a fifth initial charge and discharge cycle was used ashigh-temperature storage characteristics. (High-temperature storagecharacteristics (%)=A (mAh)/B (mAh)×100)

Example J1

A flake natural graphite having a d50 of 100 μm was crushed with a dryswirl-flow crusher to give a flake natural graphite having a d50 of 8.1μm, a Tap of 0.39 g/cm³, and a water content of 0.08% by mass. To 100 gof the resulting flake natural graphite, 12 g of a granulating agent ofan aromatic oil I (aniline point, 29° C.; containing a naphthalene ringstructure in its molecule) was added and mixed with stirring. The sampleobtained was disintegrated and mixed using a hammer mill (MF10 availablefrom IKA) at a rotation speed of 3,000 rpm to give a flake naturalgraphite to which the granulating agent uniformly adhered. Using a ModelNHS-1 hybridization system available from Nara Machinery Co., Ltd., thesample obtained was mechanically spheroidized at a rotor peripheralspeed of 85 m/sec for 10 minutes to give granulated carbon materialparticles.

The granulated carbon material particles and a coal-tar pitch, servingas a carbonaceous material precursor having lower crystallinity than theraw carbon material, were mixed using a mixer at 120° C. for 20 minutes.The resulting mixture was heat treated in an inert gas at 1,300° C. for1 hour, and then the burned product was disintegrated and classified togive multi-layered graphite particles made of the granulated carbonmaterial particles and the carbonaceous material having lowercrystallinity than the raw carbon material combined with each other. Theburning yield showed that the mass ratio of the granulated carbonmaterial particles to the carbonaceous material having lowercrystallinity than the raw carbon material (granulated carbon materialparticle/amorphous carbon) of the multi-layered graphite particles was1:0.065. The d50, SA, Tap, discharge capacity, low-temperature outputcharacteristics, and high-temperature storage characteristics of thesample obtained were measured. The results are shown in Table 1J.

Example J2

Multi-layered graphite particles were obtained in the same manner as inExample J1 except that the mass ratio of the granulated carbon materialparticles to the carbonaceous material having lower crystallinity thanthe raw carbon material (granulated carbon material particle/amorphouscarbon) was 1:0.08. The results of the measurements made in the samemanner as in Example J1 are shown in Table 1J.

Example J3

Multi-layered graphite particles were obtained in the same manner as inExample J2 except that an aromatic oil II (aniline point, none; mixedaniline point, 15° C.; containing a benzene ring structure in itsmolecule) was used as a granulating agent. The results of themeasurements made in the same manner as in Example J1 are shown in Table1J.

Reference Example J1

Multi-layered graphite particles were obtained in the same manner as inExample J1 except that a paraffinic oil (aniline point, >100° C.) wasused as a granulating agent. The results of the measurements made in thesame manner as in Example J1 are shown in Table 1J.

Reference Example J2

Multi-layered graphite particles were obtained in the same manner as inComparative Example J1 except that the mass ratio of the granulatedcarbon material particles to the carbonaceous material having lowercrystallinity than the raw carbon material (granulated carbon materialparticle/amorphous carbon) was 1:0.08. The results of the measurementsmade in the same manner as in Example J1 are shown in Table 1J.

Reference Example J3

Multi-layered graphite particles were obtained in the same manner as inComparative Example J1 except that the mass ratio of the granulatedcarbon material particles to the carbonaceous material having lowercrystallinity than the raw carbon material (granulated carbon materialparticle/amorphous carbon) was 1:0.1. The results of the measurementsmade in the same manner as in Example J1 are shown in Table 1J.

Comparative Example J1

A flake natural graphite having a d50 of 100 μm was mechanicallyspheroidized as it is at a rotor peripheral speed of 85 m/sec for 10minutes using a Model NHS-1 hybridization system available from NaraMachinery Co., Ltd. In the sample obtained was confirmed the presence ofa large amount of flake graphite fine powder not deposited on the basematerial or incorporated into the spheroidized particles. This samplewas classified to remove the flake graphite fine powder, therebyproviding a spheroidized graphite having a d50 of 10.8 μm and a Tapdensity of 0.88 g/cm³. The spheroidized graphite and a coal-tar pitch,serving as a carbonaceous material precursor having lower crystallinitythan the raw carbon material, were mixed using a mixer at 120° C. for 20minutes. The resulting mixture was heat treated in an inert gas at1,300° C. for 1 hour, and then the burned product was disintegrated andclassified to give multi-layered graphite particles made of thegranulated carbon material particles and the carbonaceous materialhaving lower crystallinity than the raw carbon material combined witheach other. The burning yield showed that the mass ratio of thegranulated carbon material particles to the carbonaceous material havinglower crystallinity than the raw carbon material (granulated carbonmaterial particle/amorphous carbon) of the multi-layered graphiteparticles was 1:0.065. The d50, SA, Tap, discharge capacity,low-temperature output characteristics, and high-temperature storagecharacteristics of the sample obtained were measured. The results areshown in Table 1J.

TABLE 1J Low- High- Temper- Temper- ature ature Output Storage Charac-Charac- teristics, teristics, Tap, Discharge (Reference (Reference d50,g/ SA, Capacity, Example Example μm cm³ m²/g mAh/g J2 = 100) J2 = 100)Example J1 11.8 1.02 7.8 362 109.9 98.9 Example J2 12.0 0.92 6.1 359104.8 100.4 Example J3 11.9 0.94 5.8 359 103.1 101.1 Reference 12.0 1.057.9 362 94.4 98.6 Example J1 Reference 11.8 1.02 7.1 359 100.0 100.0Example J2 Reference 12.0 0.92 5.7 357 91.2 100.4 Example J3 Comparative11.4 1.04 3.1 362 68.1 104.4 Example J1

In Examples J1 to J3, the low-temperature output characteristics and thehigh-temperature storage characteristics were sufficiently superior tothose in Reference Examples J1 to J3 and Comparative Example J1.

Eleventh examples (Examples K) of the present invention will now bedescribed.

Preparation of Electrode Sheet

An electrode plate having an active material layer with an activematerial layer density of 1.35±0.03 g/cm³ was prepared using graphiteparticles of Examples or Comparative Examples. Specifically, 50.00±0.02g of a negative electrode material, 50.00±0.02 g (0.500 g on a solidsbasis) of a 1% by mass aqueous carboxymethylcellulose sodium saltsolution, and 0.5 g (on a solids basis) of an aqueous dispersion of astyrene-butadiene rubber having a weight average molecular weight of270,000 were stirred with a Keyence hybrid mixer for 5 minutes, and themixture was defoamed for 30 seconds to give a slurry.

The slurry was applied to a 10-μm-thick copper foil, serving as acurrent collector, to a width of 10 cm using a small die coateravailable from Itochu Machining Co., Ltd. such that the negativeelectrode material adhered in an amount of 6.0±0.3 mg/cm² or 12.0±0.3mg/cm². The coated foil was roll-pressed using a roller having adiameter of 20 cm to adjust the density of the active material layer tobe 1.35±0.03 g/cm³, thereby preparing an electrode sheet.

Production of Non-Aqueous Secondary Battery (2016 Coin Battery)

The electrode sheet prepared by the above-described method, to which thenegative electrode material adhered in an amount of 12.0±0.3 mg/cm² andin which the density of the active material layer was 1.35±0.03 g/cm³,was cut into a disk having a diameter of 12.5 mm, and lithium metal foilwas cut into a disk having a diameter of 14 mm to prepare a counterelectrode. A separator (made of a porous polyethylene film) was placedbetween the two electrodes, the separator being impregnated with anelectrolyte solution of 1 mol/L of LiPF₆ in a mixed solvent of ethylenecarbonate and ethyl methyl carbonate (volume ratio=3:7). In this manner,2016 coin batteries were produced.

Method of Producing Non-Aqueous Secondary Battery (Laminate Battery)

The electrode sheet prepared by the above-described method, to which thenegative electrode material adhered in an amount of 6.0±0.3 mg/cm² andin which the density of the active material layer was 1.35±0.03 g/cm³,was cut to 4 cm×3 cm to prepare a negative electrode, and a positiveelectrode made of NMC was cut to the same area. The negative electrodeand the positive electrode were combined with a separator (made of aporous polyethylene film) placed therebetween. An electrolyte solutionof 1.2 mol/L of LiPF₆ in a mixed solvent of ethylene carbonate, ethylmethyl carbonate, and dimethyl carbonate (volume ratio=3:3:4) wasinjected in an amount of 200 μL to produce a laminate battery.

Method for Measuring Discharge Capacity

Using the non-aqueous secondary battery (2016 coin battery) produced bythe above-described method, the capacity of the battery during chargingand discharging was measured by the following method.

The lithium counter electrode was charged to 5 mV at a current densityof 0.05 C and further charged at a constant voltage of 5 mV to a currentdensity of 0.005 C. The negative electrode was doped with lithium, andthen the lithium counter electrode was discharged to 1.5 V at a currentdensity of 0.1 C. Subsequently, a second charging and discharging wasperformed at the same current density. The discharge capacity at thesecond cycle was defined as a discharge capacity of this battery.

Low-Temperature Output Characteristics

Using the laminate non-aqueous electrolyte secondary battery produced bythe method for producing a non-aqueous electrolyte secondary batterydescribed above, low-temperature output characteristics were measured bythe following method.

A non-aqueous electrolyte secondary battery that had yet to go through acharge and discharge cycle was subjected to an initial charge anddischarge that involves three cycles in a voltage range of 4.1 V to 3.0V at 25° C. and a current of 0.2 C (1 C is a current at which a ratedcapacity at a 1-hour rate discharge capacity is discharged in 1 hour,and so on) and two cycles in a voltage range of 4.2 V to 3.0 V at acurrent of 0.2 C (in charging, a constant-voltage charge at 4.2 V wasfurther performed for 2.5 hours).

Furthermore, charging was performed at a current of 0.2 C to an SOC of50%, and then constant-current discharging was performed in alow-temperature environment at −30° C. for 2 seconds at varying currentsof ⅛ C, ¼ C, ½ C, 1.5 C, and 2 C. The battery voltage drop at 2 secondsafter discharging under each condition was measured. From eachmeasurement, a current I that could be passed in 2 seconds when theupper limit charge voltage was 3 V was calculated, and a valuecalculated from the formula: 3×I (W) was defined as the low-temperatureoutput characteristics of each battery.

a: Volume-Based Average Particle Diameter (d50)

The d50 was determined as a volume-based median diameter by suspending0.01 g of a carbon material in 10 mL of a 0.2% by mass aqueous solutionof a polyoxyethylene sorbitan monolaurate surfactant (Tween 20(registered trademark)), placing the suspension (a measurement sample)in a commercially available laser diffraction/scattering particle sizedistribution analyzer (e.g., LA-920 available from HORIBA, Ltd.),irradiating the measurement sample with ultrasonic waves of 28 kHz at apower of 60 W for 1 minute, and then performing a measurement with theanalyzer.

x_(k): True Density

The true density of a carbon material sample was measured by pycnometryusing a true density meter (MAT-7000 Auto True Denser available fromSeishin Enterprise Co., Ltd).

Density Under Uniaxial Load of 100 Kgf/3.14 cm²

The density under a uniaxial load of 100 kgf/3.14 cm² was measured usingan MCP-PD51 powder resistivity measurement system available fromMitsubishi Chemical Analytech Co., Ltd. First, values of the apparatuswere corrected. For a load correction, the load measured when the bottomof a cylindrical container for accommodating the carbon material and apush rod to be inserted into the container from above to apply pressureto the carbon material were separated from each other was confirmed tobe 0 kgf/3.14 cm². Next, a thickness gauge was corrected. While thecylindrical container and the push rod were brought close using ahydraulic pump, a zero-point correction was carried out such that thethickness gauge indicated 0.00 mm when the load reached 20 kgf/3.14 cm².After the corrections were carried out, 3.0 g of the carbon material wasplaced in the cylindrical container with a diameter of 2 cm, and theheight of the carbon material was adjusted so as to receive a loadevenly. A seat was lifted using the hydraulic pump, and the push rod wasinserted into the cylindrical container. After the thickness gauge hadindicated 15.0 mm, loads were measured at thicknesses at 0.5-mmintervals until the load exceeded 1,000 kgf/3.14 cm². From thethicknesses obtained, the densities of the powder were calculated, andusing Microsoft Excel, a graph was created with powder density plottedon the horizontal axis and load on the vertical axis. A cubic splinecurve of the graph was created, and the formula obtained was used tocalculate a carbon material density under a load of 100 kgf/3.14 cm³. Toreduce variation in measurements, the measurement was made at leasttwice. When variation occurred, the measurement was made three times,and the average of two closest values was used.

Tap Density: Tap

Using a powder density meter, the carbon material of the presentinvention was dropped through a sieve with openings of 300 μm into acylindrical tap cell with a diameter of 1.6 cm and a volume capacity of20 cm³ to fill up the cell, and then a tap with a stroke length of 10 mmwas given 1,000 times. The density calculated from the volume at thistime and the mass of the sample was defined as the tap density.

y_(k): Density Under Uniaxial Load of 100 Kgf/3.14 cm²—Tap Density

y_(k) is a value obtained by subtracting a tap density from a densityunder a uniaxial load of 100 kgf/3.14 cm².

Example K1

A flake natural graphite having a d50 of 100 μm was crushed with a dryswirl-flow crusher to give a flake natural graphite having a d50 of 8.1μm, a tap density of 0.39 g/cm³, and a water content of 0.08% by mass.To 100 g of the resulting flake natural graphite, 12 g of a granulatingagent of a paraffinic oil (liquid paraffin available from Wako PureChemical Industries, Ltd., first grade, physical properties at 25° C.:viscosity=95 cP, contact angle=13.2°, surface tension=31.7 mN/m, r cosθ=30.9) was added and mixed with stirring. The sample obtained wasdisintegrated and mixed using a hammer mill (MF10 available from IKA) ata rotation speed of 3,000 rpm to give a flake natural graphite to whichthe granulating agent uniformly adhered. Using a Model NHS-1hybridization system available from Nara Machinery Co., Ltd., the flakenatural graphite to which the granulating agent uniformly adhered wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes while fine powder generated during the spheroidization wasdeposited on the base material and incorporated into the spheroidizedparticles, and heat treated in an inert gas at 720° C. to give aspheroidized graphite having a d50 of 13 μm.

The spheroidized natural graphite and a coal-tar pitch, serving as anamorphous carbon precursor, were mixed and heat treated in an inert gasat 1,300° C., and then the burned product was disintegrated andclassified to give a multi-layered carbon material made of graphiteparticles and an amorphous carbon combined with each other. The burningyield showed that the mass ratio of the granulated graphite particles tothe carbonaceous material having lower crystallinity than the rawgraphite (granulated graphite particle/amorphous carbon) of themulti-layered graphite particles was 1:0.065. The true density, d50, tapdensity, density under a uniaxial load of 100 kgf/3.14 cm², dischargecapacity, and low-temperature output characteristics of the sampleobtained were measured. The results are shown in Table 1K.

Example K2 Multi-layered graphite particles were obtained in the samemanner as in Example K1 except that the mass ratio of the granulatedgraphite particles to the carbonaceous material having lowercrystallinity than the raw graphite (granulated graphiteparticle/amorphous carbon) of the multi-layered graphite particles was1:0.08. The results of the measurements made in the same manner as inExample K1 are shown in Table 1K.

Comparative Example K1

A spheroidized natural graphite was prepared in the same manner as inExample K1 except that no granulating agent was added, and thespheroidized natural graphite was air classified to remove the flakegraphite fine powder that had not been granulated, thereby providing aspheroidized natural graphite having a d50 of 10.9 μm and a Tap densityof 0.88 g/cm³. The spheroidized natural graphite and a petroleum-derivedheavy oil, serving as an amorphous carbon precursor, were mixed and heattreated in an inert gas at 1,300° C., and then the burned product wasdisintegrated and classified to give a multi-layered carbon materialmade of graphite particles and an amorphous carbon combined with eachother. The burning yield showed that the mass ratio of spheroidizedgraphite particle to amorphous carbon (spheroidized graphiteparticle/amorphous carbon) of the multi-layered carbon material was1:0.02. The results of the measurements made in the same manner as inExample K1 are shown in Table 1K.

Comparative Example K2

A multi-layered carbon material was obtained in the same manner exceptthat the mixing ratio of the petroleum-derived heavy oil was changedfrom that in Comparative Example K1. The burning yield showed that themass ratio of spheroidized graphite particle to amorphous carbon(spheroidized graphite particle/amorphous carbon) of the multi-layeredcarbon material was 1:0.04. The results of the measurements made in thesame manner as in Example K1 are shown in Table 1K.

Comparative Example K3

A multi-layered carbon material was obtained in the same manner exceptthat the mixing ratio of the petroleum-derived heavy oil was changedfrom that in Comparative Example K1. The burning yield showed that themass ratio of spheroidized graphite particle to amorphous carbon(spheroidized graphite particle/amorphous carbon) of the multi-layeredcarbon material was 1:0.05. The results of the measurements made in thesame manner as in Example K1 are shown in Table 1K.

Comparative Example K4

A multi-layered carbon material was obtained in the same manner as inComparative Example K1 except that a coal-tar pitch was used as anamorphous carbon precursor in place of the petroleum-derived heavy oil,and its mixing ratio was changed. The burning yield showed that the massratio of spheroidized graphite particle to amorphous carbon(spheroidized graphite particle/amorphous carbon) of the multi-layeredcarbon material was 1:0.07. The results of the measurements made in thesame manner as in Example K1 are shown in Table 1K.

Example K3

A flake natural graphite having a d50 of 100 μm was crushed with amechanical crusher having a crushing rotor and a liner to give a flakenatural graphite having a d50 of 30 μm and a water content of 0.03% bymass. To 100 g of the resulting flake natural graphite, 6 g of agranulating agent of a paraffinic oil (liquid paraffin available fromWako Pure Chemical Industries, Ltd., first grade, physical properties at25° C.: viscosity=95 cP, contact angle=13.2°, surface tension=31.7 mN/m,r cos θ=30.9) was added and mixed with stirring. The sample obtained wasdisintegrated and mixed using a hammer mill (MF10 available from IKA) ata rotation speed of 3,000 rpm to give a flake natural graphite to whichthe granulating agent uniformly adhered. Using a Model NHS-1hybridization system available from Nara Machinery Co., Ltd., the flakenatural graphite to which the granulating agent uniformly adhered wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes while fine powder generated during the spheroidization wasdeposited on the base material and incorporated into the spheroidizedparticles, thereby providing a spheroidized natural graphite having ad50 of 19.4 μm. The spheroidized natural graphite and a coal-tar pitch,serving as an amorphous carbon precursor, were mixed and heat treated inan inert gas at 1,300° C., and then the burned product was disintegratedand classified to give a multi-layered carbon material made of graphiteparticles and an amorphous carbon combined with each other. The burningyield showed that the mass ratio of spheroidized graphite particle toamorphous carbon (spheroidized graphite particle/amorphous carbon) ofthe multi-layered carbon material was 1:0.03. The results of themeasurements made in the same manner as in Example K1 are shown in Table1K.

Example K4

The spheroidized natural graphite obtained in Example K3 and a coal-tarpitch, serving as an amorphous carbon precursor, were mixed and heattreated in an inert gas at 1,300° C., and then the burned product wasdisintegrated and classified to give a multi-layered carbon materialmade of graphite particles and an amorphous carbon combined with eachother. The burning yield showed that the mass ratio of spheroidizedgraphite particle to amorphous carbon (spheroidized graphiteparticle/amorphous carbon) of the multi-layered carbon material was1:0.04. The results of the measurements made in the same manner as inExample K1 are shown in Table 1K.

Example K5

The spheroidized natural graphite obtained in Example K3 and a coal-tarpitch, serving as an amorphous carbon precursor, were mixed and heattreated in an inert gas at 1,300° C., and then the burned product wasdisintegrated and classified to give a multi-layered carbon materialmade of graphite particles and an amorphous carbon combined with eachother. The burning yield showed that the mass ratio of spheroidizedgraphite particle to amorphous carbon (spheroidized graphiteparticle/amorphous carbon) of the multi-layered carbon material was1:0.05. The results of the measurements made in the same manner as inExample K1 are shown in Table 1K.

Example K6

The spheroidized natural graphite obtained in Example K1 and a coal-tarpitch, serving as an amorphous carbon precursor, were mixed and heattreated in an inert gas at 1,300° C., and then the burned product wasdisintegrated and classified to give a multi-layered carbon materialmade of graphite particles and an amorphous carbon combined with eachother. The burning yield showed that the mass ratio of spheroidizedgraphite particle to amorphous carbon (spheroidized graphiteparticle/amorphous carbon) of the multi-layered carbon material was1:0.10. The results of the measurements made in the same manner as inExample K1 are shown in Table 1K.

Comparative Example K5

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 3minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite and flake graphite fine powder generated duringthe spheroidization that were not deposited on the base material orincorporated. This sample was classified to remove the flake graphitefine powder, thereby providing a spheroidized graphite having a d50 of19 μm. The spheroidized natural graphite and a coal-tar pitch, servingas an amorphous carbon precursor, were mixed and heat treated in aninert gas at 1,300° C., and then the burned product was disintegratedand classified to give a multi-layered carbon material made of graphiteparticles and an amorphous carbon combined with each other. The burningyield showed that the mass ratio of spheroidized graphite particle toamorphous carbon (spheroidized graphite particle/amorphous carbon) ofthe multi-layered carbon material was 1:0.01. The results of themeasurements made in the same manner as in Example K1 are shown in Table1K.

Comparative Example K6

A multi-layered carbon material was obtained in the same manner exceptthat the mixing ratio of the coal-tar pitch was changed from that inComparative Example K5. The burning yield showed that the mass ratio ofspheroidized graphite particle to amorphous carbon (spheroidizedgraphite particle/amorphous carbon) of the multi-layered carbon materialwas 1:0.03.

The results of the measurements made in the same manner as in Example K1are shown in Table 1K.

Comparative Example K7

A multi-layered carbon material was obtained in the same manner exceptthat the mixing ratio of the coal-tar pitch was changed from that inComparative Example K5. The burning yield showed that the mass ratio ofspheroidized graphite particle to amorphous carbon (spheroidizedgraphite particle/amorphous carbon) of the multi-layered carbon materialwas 1:0.06.

The results of the measurements made in the same manner as in Example K1are shown in Table 1K.

Comparative Example K8

A multi-layered carbon material was obtained in the same manner exceptthat the mixing ratio of the coal-tar pitch was changed from that inComparative Example K5. The burning yield showed that the mass ratio ofspheroidized graphite particle to amorphous carbon (spheroidizedgraphite particle/amorphous carbon) of the multi-layered carbon materialwas 1:0.08.

The results of the measurements made in the same manner as in Example K1are shown in Table 1K.

TABLE 1K Low-Temperature Output X_(k) Density Right RightCharacteristics True a under 100 Side of Side of Discharge (ComparativeDensity d50 Tap kgf/3.14 Y_(k) Inequality Inequality Capacity Example K4= 100) (g/cm³) (μm) (g/cm³) cm² (g/cm³) (g/cm³) (1K) (3K) (mAh/g) (%)Example K1 2.23 12 1.05 1.24 0.19 10.868 10.972 362 139 Example K2 2.2312 1.02 1.25 0.24 10.817 10.920 359 147 Comparative 2.25 11 0.99 1.230.24 10.923 11.020 368 111 Example K1 Comparative 2.24 11 1.03 1.21 0.1810.931 11.029 365 103 Example K2 Comparative 2.24 11 1.04 1.20 0.1610.934 11.033 363 102 Example K3 Comparative 2.23 11 1.04 1.18 0.1410.927 11.026 361 100 Example K4 Example K3 2.25 18 1.16 1.34 0.1810.896 11.052 366 118 Example K4 2.24 18 1.19 1.34 0.15 10.896 11.056363 124 Example K5 2.24 19 1.18 1.35 0.16 10.864 11.033 363 124 ExampleK6 2.22 22 1.19 1.31 0.12 10.796 10.991 358 113 Comparative 2.25 18 1.141.31 0.18 10.935 11.095 367 91 Example K5 Comparative 2.25 19 1.17 1.290.12 10.961 11.128 367 93 Example K6 Comparative 2.24 19 1.19 1.28 0.0910.960 11.127 364 79 Example K7 Comparative 2.23 19 1.21 1.28 0.0710.920 11.087 358 67 Example K8

In Examples K1 to K6, values of the right side of inequality (1K) areless than 10.914, showing that the capacity and the low-temperatureoutput characteristics were superior to those of Comparative Examples K1to K8, where values of the right side of inequality (1K) are greaterthan 10.914. Furthermore, in Examples K1 to K2, values of the right sideof inequality (3K) are less than 10.990, showing that the capacity andthe low-temperature output are very excellent.

Twelfth examples (Examples L) of the present invention will now bedescribed.

Preparation of Electrode Sheet

An electrode plate having an active material layer with an activematerial layer density of 1.60±0.03 g/cm³ was prepared using graphiteparticles of Examples or Comparative Examples. Specifically, 50.00±0.02g of a negative electrode material, 50.00±0.02 g (0.500 g on a solidsbasis) of a 1% by mass aqueous carboxymethylcellulose sodium saltsolution, and 1.00±0.05 g (0.5 g on a solids basis) of an aqueousdispersion of a styrene-butadiene rubber having a weight averagemolecular weight of 270,000 were stirred with a Keyence hybrid mixer for5 minutes, and the mixture was defoamed for 30 seconds to give a slurry.

The slurry was applied to a 10-μm-thick copper foil, serving as acurrent collector, to a width of 10 cm using a small die coateravailable from Itochu Machining Co., Ltd. such that the negativeelectrode material adhered in an amount of 12.00±0.3 mg/cm². The coatedfoil was roll-pressed using a roller having a diameter of 20 cm toadjust the density of the active material layer to be 1.60±0.03 g/cm³,thereby preparing an electrode sheet.

Production of Non-Aqueous Secondary Battery (2016 Coin Battery)

The electrode sheet prepared by the above-described method was cut intoa disk having a diameter of 12.5 mm, and lithium metal foil was cut intoa disk having a diameter of 14 mm to prepare a counter electrode. Aseparator (made of a porous polyethylene film) was placed between thetwo electrodes, the separator being impregnated with an electrolytesolution of 1 mol/L of LiPF₆ in a mixed solvent of ethylene carbonateand ethyl methyl carbonate (volume ratio=3:7). In this manner, 2016 coinbatteries were produced.

Method of Producing Non-Aqueous Secondary Battery (Laminate Battery)

The electrode sheet prepared by the above-described method was cut to 4cm×3 cm to prepare a negative electrode, and a positive electrode madeof NMC was cut to the same area. The negative electrode and the positiveelectrode were combined with a separator (made of a porous polyethylenefilm) placed therebetween. An electrolyte solution of 1.2 mol/L of LiPF₆in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, anddimethyl carbonate (volume ratio=3:3:4) was injected in an amount of 250μl to produce a laminate battery.

Method for Measuring Discharge Capacity

Using the non-aqueous secondary battery (2016 coin battery) produced bythe above-described method, the capacity of the battery during chargingand discharging was measured by the following method. The lithiumcounter electrode was charged to 5 mV at a current density of 0.05 C andfurther charged at a constant voltage of 5 mV to a current density of0.005 C. The negative electrode was doped with lithium, and then thelithium counter electrode was discharged to 1.5 V at a current densityof 0.1 C. Subsequently, a second charging and discharging was performedat the same current density. The discharge capacity at the second cyclewas defined as a discharge capacity of this battery.

Low-Temperature Output Characteristics

Using the laminate non-aqueous electrolyte secondary battery produced bythe method for producing a non-aqueous electrolyte secondary batterydescribed above, low-temperature output characteristics were measured bythe following method.

A non-aqueous electrolyte secondary battery that had yet to go through acharge and discharge cycle was subjected to an initial charge anddischarge that involves three cycles in a voltage range of 4.1 V to 3.0V at 25° C. and a current of 0.2 C (1 C is a current at which a ratedcapacity at a 1-hour rate discharge capacity is discharged in 1 hour,and so on) and two cycles in a voltage range of 4.2 V to 3.0 V at acurrent of 0.2 C (in charging, a constant-voltage charge at 4.2 V wasfurther performed for 2.5 hours).

Furthermore, charging was performed at a current of 0.2 C to an SOC of50%, and then constant-current discharging was performed in alow-temperature environment at −30° C. for 2 seconds at varying currentsof ⅛ C, ¼ C, ½ C, 1.5 C, and 2 C. The battery voltage drop at 2 secondsafter discharging under each condition was measured. From eachmeasurement, a current I that could be passed in 2 seconds when theupper limit charge voltage was 3 V was calculated, and a valuecalculated from the formula: 3×I (W) was defined as the low-temperatureoutput characteristics of each battery.

Roundness R Determined with Flow-Type Particle Image Analyzer

Using a flow-type particle image analyzer (FPIA-2000 available fromSysmex Corporation), a particle size distribution based on equivalentcircle diameter was measured, and a roundness was determined.Ion-exchanged water was used as a dispersion medium, and polyoxyethylene(20) monolaurate was used as a surfactant. The equivalent circlediameter is a diameter of a circle (equivalent circle) having the sameprojected area as that of a captured particle image, and the roundnessis a ratio of the perimeter of the equivalent circle, as the numerator,to the perimeter of the captured particle projection image, as thedenominator. Roundnesses of particles having an equivalent diameter inthe range of 1.5 to 40 μm were averaged to determine the roundness R.

Volume-Based Average Particle Diameter X Determined by LaserDiffraction: d50

The d50 was determined as a volume-based median diameter (d50) bysuspending 0.01 g of a carbon material in 10 mL of a 0.2% by massaqueous solution of a polyoxyethylene sorbitan monolaurate surfactant(Tween 20 (registered trademark)), placing the suspension (a measurementsample) in a commercially available laser diffraction/scatteringparticle size distribution analyzer (e.g., LA-920 available from HORIBA,Ltd.), irradiating the measurement sample with ultrasonic waves of 28kHz at a power of 60 W for 1 minute, and then performing a measurementwith the analyzer.

Tap Density

Using a powder density meter, the carbon material of the presentinvention was dropped through a sieve with openings of 300 μm into acylindrical tap cell with a diameter of 1.6 cm and a volume capacity of20 cm³ to fill up the cell, and then a tap with a stroke length of 10 mmwas given 1,000 times. The density calculated from the volume at thistime and the mass of the sample was defined as the tap density.

Acquisition of Cross-Sectional SEM Image

The cross-sectional SEM image of the carbon material was measured asdescribed below. As an electrode plate containing the carbon materialwas used the same electrode plate as used to produce the above-describedbattery for performance evaluation. First, an electrode cross sectionwas processed using a cross section polisher (IB-09020CP available fromJEOL Ltd). From the processed electrode cross-section, a reflectedelectron image was acquired with an SEM (SU-70 available from HitachiHigh-Technologies Corporation). The SEM observation was carried outunder the conditions of an acceleration voltage of 10 kV and amagnification of 1,000× to obtain an image that enables the acquisitionof one particle at a resolution of 256 dpi. After that, in accordancewith the above-described method and conditions for measuring dispersity,30 or more particles satisfying |X₁−X|/X₁≦0.2 and |R−R₁|≦0.1 wereselected using two SEM images of 150 μm×100 μm. Moreover, 30 particleseach having graphite portions with an average luminance of 80 or greaterand void portions with an average luminance of 65 or less were selectedas binarizable images.

Establishment of Particle Boundary

Using image processing software imageJ, a particle boundary wasestablished by an approximation by a polygon. The approximation was madeby a polygon with 15 or more sides to the particle shape. Thenon-particle region was processed so as to have a luminance of 255 atevery pixel.

Binarization of Cross-Sectional SEM Image (Division into Void Regionsand Non-Void Regions)

Void regions and non-void regions of the carbon material observed in thecross-sectional SEM image were binarized using image software imageJwith a threshold set to a luminance of 80 to 85.

Equivalent Circular Diameter X₁ Determined from Cross-Sectional SEMImage

The equivalent circular diameter X₁ was calculated by the followingformula, where L is a particle circumference [μm], that is, the totallength of line segments of a polygonal particle boundary.

$\begin{matrix}{X_{1} = \frac{L}{2\pi}} & \left\lbrack {{Mathematical}\mspace{14mu} 17} \right\rbrack\end{matrix}$

Roundness R₁ Determined from Cross-Sectional SEM Image

The roundness R₁ was calculated by the following formula using theparticle circumference L obtained above, where S is an area of thepolygon defined by the particle boundary.

$\begin{matrix}{R_{1} = \frac{4\pi \; S}{(L)^{2}}} & \left\lbrack {{Mathematical}\mspace{14mu} 18} \right\rbrack\end{matrix}$

Box-Counting Dimension Relative to Void Regions

Since the maximum length of the image obtained was about 260 pixel,analyses were carried out at Box sizes of 2, 3, 4, 6, 8, 16, 32, and 64.For the 30 randomly selected particles satisfying |x₁−X|/X₁≦0.2 and|R−R₁|≦0.1 in the cross-sectional SEM image, box-counting dimensionsrelative to void regions were calculated and averaged to determine theaverage box-counting dimension relative to void regions.

Average Dispersity D

In the cross-sectional SEM image, 30 granulated particles satisfying|X₁−X|/X₁≦0.2 and |R−R₁|≦0.1 were randomly selected, and for eachparticle, the dispersity D given by equation (B) was calculated. Thedispersities D of the 30 particles were averaged. The expectation E ofthe void area in a target compartment is calculated by equation (A).

Dispersity D (%)=(sum total [μm²] of areas of compartments that satisfy(gross area [μm²] of voids in target compartment)/(expectation E [μm²]of void area in target compartment)=0.5 or greater)/(sum total [μm²] ofareas of all the compartments of one target granulatedparticle)×100  Equation (B)

Expectation E [μm²] of void area in target compartment=(gross area [μm²]of internal voids of one target granulated particle)/(cross-sectionalarea [μm²] of one target granulated particle)×(area [μm²] of targetcompartment)  Equation (A)

Zave/X

In the cross-sectional SEM image, 30 granulated particles satisfying|X₁−X|/X₁≦0.2 and |R−R₁|≦0.1 were randomly selected, and for eachparticle, the inter-void distance Z was calculated as described below.The average (Zave) of the inter-void distances Z of the 30 particles wascalculated, and the ratio of the average to the volume-based averageparticle diameter X determined by laser diffraction (Zave/X) wascalculated.

Definition of Average Inter-Void Distance Z (Zave) of 30 Particles

Three lines were drawn that were parallel to the minor axis of thegranulated particle and split the major axis of the granulated particleinto four parts, and inter-void distances Z (μm) of the granulatedparticle on each line were each measured. The average of 30 particles intotal was calculated. This was defined as the average inter-voiddistance Z (Zave) of 30 particles.

W/X

For each of the 30 particles selected in calculating Zave/X, the voidsize Y was calculated as described below. The standard deviation (W) ofthe void sizes Y of the 30 particles was calculated, and the ratio ofthe standard deviation to the volume-based average particle diameter Xdetermined by laser diffraction (W/X) was calculated.

Definition of Standard Deviation (W) of Void Sizes Y (μm) of 30Particles

Three lines were drawn that were parallel to the minor axis of thegranulated particle and split the major axis of the granulated particleinto four parts, and void sizes Y (μm) of the granulated particle oneach line were each measured. The standard deviation of 30 particles intotal was calculated. This was defined as the standard deviation (W) ofvoid sizes Y of 30 particles.

The standard deviation was determined by the following formula, whereYave is the average of Y, and Ny is the number of Y.

$\begin{matrix}{W = \left( \frac{\sum\left( {Y - Y_{ave}} \right)^{2}}{Ny} \right)^{1/2}} & \left\lbrack {{Mathematical}\mspace{14mu} 19} \right\rbrack\end{matrix}$

The Number (Percentage) of Particles Having Voids Arranged in Layers

Among the 30 particles selected in calculating Zave/X, the number ofparticles was counted in which the proportion of the area of slit-likevoids in layers (the area of voids in layers/the gross area of voids)was 50% or more, and the proportion of the number of slit-like voids(the number of slit-like voids/the total number of voids) was 70% ormore, as observed in the cross-sectional SEM image. The percentage inthe 30 particles was calculated.

Example L1

A flake natural graphite having a d50 of 100 μm was crushed with a dryswirl-flow crusher to give a flake natural graphite having a d50 of 8.1μm, a Tap of 0.39 g/cm³, and a water content of 0.08% by mass. To 100 gof the resulting flake natural graphite, 12 g of a granulating agent ofa liquid paraffin (Wako Pure Chemical Industries, Ltd., first grade,physical properties at 25° C.: viscosity=95 cP, contact angle=13.2°,surface tension=31.7 mN/m, r cos θ=30.9) was added and mixed withstirring. The sample obtained was disintegrated and mixed using a hammermill (MF10 available from IKA) at a rotation speed of 3,000 rpm to givea flake natural graphite to which the granulating agent adhered. Using aModel NHS-1 hybridization system available from Nara Machinery Co.,Ltd., the flake natural graphite to which the granulating agentuniformly adhered was mechanically spheroidized at a rotor peripheralspeed of 85 m/sec for 10 minutes while fine powder generated during thespheroidization was deposited on the base material and incorporated intothe spheroidized particles, and heat treated in an inert gas at 720° C.to give a spheroidized graphite having a d50 of 12.9 μm. Using themeasurement methods described above, d50, Tap, roundness, averagebox-counting dimension, average dispersity D, Zave/X, W/X, the number(percentage) of particles having voids arranged in layers, dischargecapacity, and low-temperature output characteristics were measured. Theresults are shown in Tables 1L and 2L.

Example L2

A flake natural graphite having a d50 of 100 μm was crushed with a dryair-flow crusher to give a flake natural graphite having a d50 of 6 μm,a Tap of 0.13 g/cm³, and a water content of 0.08% by mass. To 100 g ofthe resulting flake natural graphite, 12 g of a granulating agent of aparaffinic oil (liquid paraffin available from Wako Pure ChemicalIndustries, Ltd., first grade, physical properties at 25° C.:viscosity=95 cP, contact angle=13.2°, surface tension=31.7 mN/m, r cosθ=30.9) was added and mixed with stirring. The sample obtained wasdisintegrated and mixed using a hammer mill (MF10 available from IKA) ata rotation speed of 3,000 rpm to give a flake natural graphite to whichthe granulating agent uniformly adhered. Using a Model NHS-1hybridization system available from Nara Machinery Co., Ltd., the flakenatural graphite to which the granulating agent uniformly adhered wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes while fine powder generated during the spheroidization wasdeposited on the base material and incorporated into the spheroidizedparticles, and heat treated in an inert gas at 720° C. to give aspheroidized graphite having a d50 of 9.2 μm. The results of themeasurements made in the same manner as in Example L1 are shown inTables 1L and 2L.

Example L3

A flake natural graphite having a d50 of 100 μm was crushed with a dryswirl-flow crusher to give a flake natural graphite having a d50 of 6μm, a Tap of 0.38 g/cm³, and a water content of 0.08% by mass. To 100 gof the resulting flake natural graphite, 12 g of a granulating agent ofa paraffinic oil (liquid paraffin available from Wako Pure ChemicalIndustries, Ltd., first grade, physical properties at 25° C.:viscosity=95 cP, contact angle=13.2°, surface tension=31.7 mN/m, r cosθ=30.9) was added and mixed with stirring. The sample obtained wasdisintegrated and mixed using a hammer mill (MF10 available from IKA) ata rotation speed of 3,000 rpm to give a flake natural graphite to whichthe granulating agent uniformly adhered. Using a Model NHS-1hybridization system available from Nara Machinery Co., Ltd., the flakenatural graphite to which the granulating agent uniformly adhered wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes while fine powder generated during the spheroidization wasdeposited on the base material and incorporated into the spheroidizedparticles, and heat treated in an inert gas at 720° C. to give aspheroidized graphite having a d50 of 9.9 μm. The results of themeasurements made in the same manner as in Example L1 are shown inTables 1L and 2L.

Comparative Example L1

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically spheroidized at a rotor peripheral speed of 85 m/sec for 10minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite fine powder not deposited on the base materialor incorporated into the spheroidized particles. This sample wasclassified to remove the flake graphite fine powder, thereby providing aspheroidized graphite having a d50 of 10.8 μm. The results of themeasurements made in the same manner as in Example L1 are shown inTables 1L and 2L.

Comparative Example L2

Using a Model NHS-1 hybridization system available from Nara MachineryCo., Ltd., a flake natural graphite having a d50 of 100 μm wasmechanically granulated at a rotor peripheral speed of 85 m/sec for 5minutes. In the sample obtained was confirmed the presence of a largeamount of flake graphite fine powder not deposited on the base materialor incorporated into the granulated particles. This sample wasclassified to remove the flake graphite fine powder, thereby providing agranulated carbon material having a d50 of 15.4 μm. The results of themeasurements made in the same manner as in Example L1 are shown inTables 1L and 2L.

TABLE 1L Number (Percentage) Average of Particles Tap Box- AverageHaving Voids d50 (g/ Counting Dispersity Arranged in (μm) cm³) RoundnessDimension D (%) Zave/X W/X Layers Example L1 12.9 0.88 0.94 1.65 700.030 0.012 28 (93%) Example L2 9.2 0.77 0.92 1.60 63 0.047 0.014 24(80%) Example L3 9.9 0.91 0.93 1.63 64 0.043 0.013 25 (83%) Comparative10.8 0.93 0.93 1.51 53 0.069 0.020  8 (27%) Example L1 Comparative 15.41.01 0.93 1.52 56 0.063 0.020  9 (30%) Example L2

TABLE 2L Low-Temperature Output Characteristics, Discharge (ComparativeCapacity Example L1 = mAh/g 100) Example L1 367 124 Example L2 365 126Example L3 362 169 Comparative 365 100 Example L1 Comparative 367 90Example L2

Example L4

The spheroidized natural graphite before heat treatment obtained inExample L1 and a coal-tar pitch, serving as an amorphous carbonprecursor, were mixed and heat treated in an inert gas at 1,300° C., andthen the burned product was disintegrated and classified to give amulti-layered carbon material made of graphite particles and anamorphous carbon combined with each other. The burning yield showed thatthe mass ratio of spheroidized graphite particle to amorphous carbon(spheroidized graphite particle/amorphous carbon) of the multi-layeredcarbon material was 1:0.08. The results of the measurements made in thesame manner as in Example L1 are shown in Tables 3L and 4L.

Comparative Example L3

The spheroidized natural graphite obtained in Comparative Example L1 anda coal-tar pitch, serving as an amorphous carbon precursor, were mixedand heat treated in an inert gas at 1,300° C., and then the burnedproduct was disintegrated and classified to give a multi-layered carbonmaterial made of graphite particles and an amorphous carbon combinedwith each other. The burning yield showed that the mass ratio ofspheroidized graphite particle to amorphous carbon (spheroidizedgraphite particle/amorphous carbon) of the multi-layered carbon materialwas 1:0.065. The results of the measurements made in the same manner asin Example L1 are shown in Tables 3L and 4L.

TABLE 3L Number (Percentage) of Particles Average Having Box- AverageVoids d50 Tap Counting Dispersity Arranged in (μm) (g/cm³) RoundnessDimension D (%) Zave/X W/X Layers Example L4 11.8 1.02 0.93 1.56 640.050 0.012 21 (70%) Comparative 11.4 1.04 0.92 1.46 49 0.075 0.020  5(17%) Example L3

TABLE 4L Low-Temperature Output Characteristics, Discharge (ComparativeCapacity Example L3 = mAh/g 100) Example L4 359 147 Comparative 362 100Example L3

INDUSTRIAL APPLICABILITY

The carbon material of the present invention, when used as an activematerial for a non-aqueous secondary battery negative electrode, canprovide a non-aqueous secondary battery having a high capacity,excellent low-temperature output characteristics, and othercharacteristics. According to the production method of the presentinvention, which involves a small number of steps, carbon materials canbe stably, efficiently, and inexpensively produced. Furthermore, carbonmaterials for non-aqueous secondary batteries having various types ofparticle structures can be stably produced.

CLAIM SCOPE AND INCORPORATED BY REFERENCE

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

1. A carbon material for a non-aqueous secondary battery, comprising agraphite capable of occluding and releasing lithium ions, the carbonmaterial having a cumulative pore volume at pore diameters in a range of0.01 μm to 1 μm of 0.08 mL/g or more, a roundness, as determined byflow-type particle image analysis, of 0.88 or greater, and a porediameter to particle diameter ratio (PD/d50(%)) of 1.8 or less, theratio being given by equation (1A):PD/d50(%)=mode pore diameter (PD) in a pore diameter range of 0.01 μm to1 μm in a pore distribution determined by mercury intrusion/volume-basedaverage particle diameter (d50)×100  (1A).
 2. A carbon material for anon-aqueous secondary battery capable of occluding and releasing lithiumions, the carbon material being formed from a plurality of graphiteparticles without being pressed and having a pore diameter to particlediameter ratio (PD/d50(%) of 1.8 or less, the ratio being given byequation (1A):PD/d50(%)=mode pore diameter (PD) in a pore diameter range of 0.01 μm to1 μm in a pore distribution determined by mercury intrusion/volume-basedaverage particle diameter (d50)×100  (1A).
 3. The carbon material for anon-aqueous secondary battery according to claim 1, wherein the carbonmaterial is a spheroidized graphite made of flake graphite, crystallinegraphite, and vein graphite and has a half width at half maximum of poredistribution (log (nm)) of 0.45 or greater, the half width at halfmaximum of pore distribution (log (nm)) referring to a half width athalf maximum at a micropore side of a peak in a pore diameter range of0.01 μm to 1 μm in a pore distribution (nm), as determined by mercuryintrusion (mercury porosimetry), of the carbon material for anon-aqueous secondary battery, with a horizontal axis expressed incommon logarithm (log (nm)).
 4. The carbon material for a non-aqueoussecondary battery according to claim 1, wherein the carbon material is acomposite carbon material comprising a spheroidized graphite made offlake graphite, crystalline graphite, and vein graphite and acarbonaceous material and has a half width at half maximum of poredistribution (log (nm)) of 0.3 or greater, the half width at halfmaximum of pore distribution (log (nm)) referring to a half width athalf maximum at a micropore side of a peak in a pore diameter range of0.01 μm to 1 μm in a pore distribution (nm), as determined by mercuryintrusion (mercury porosimetry), of the carbon material for anon-aqueous secondary battery, with a horizontal axis expressed incommon logarithm (log (nm)).
 5. The carbon material for a non-aqueoussecondary battery according to claim 1, wherein the carbon material is aspheroidized graphite made of flake graphite.
 6. The carbon material fora non-aqueous secondary battery according to claim 1, wherein the carbonmaterial has a frequency of particles with a particle diameter of 3 μmor less of 1% to 60%, the particle diameter and the frequency ofparticles being measured using a flow-type particle image analyzer afterthe carbon material has been irradiated with ultrasonic waves of 28 kHzat a power of 60 W for 5 minutes.
 7. A non-aqueous secondary batterycomprising: a positive electrode and a negative electrode, each beingcapable of occluding and releasing lithium ions; and an electrolyte, thenegative electrode comprising a current collector and a negativeelectrode active material layer on the current collector, the negativeelectrode active material layer comprising the carbon material accordingto claim
 1. 8. A method for producing a carbon material for anon-aqueous secondary battery, comprising a granulation step ofgranulating a raw carbon material by applying at least one type ofmechanical energy selected from impact, compression, friction, and shearforce, the granulation step being carried out in the presence of agranulating agent that satisfies conditions 1) and 2): 1) being liquidduring the step of granulating the raw carbon material; and 2) in thegranulating agent, no organic solvent is contained, or if contained, atleast one of the organic solvents has no flash point or a flash point of5° C. or higher.
 9. The production method according to claim 8, whereinthe granulating agent has a contact angle θ with a graphite of less than90°, the contact angle being measured by the following method: Methodfor Measuring Contact Angle θ with Graphite Onto a surface of HOPG, 1.2μL of a granulating agent is added dropwise, and when wetting andspreading has settled down and a rate of change in contact angle θ ofthe granulating agent added dropwise in one second has reached 3% orlower, the contact angle is measured using a contact angle meter (DM-501automatic contact angle meter available from Kyowa Interface ScienceCo., Ltd). When a granulating agent having a viscosity at 25° C. of 500cP or lower is used, a value at 25° C. is employed as a measurement ofthe contact angle θ, and when a granulating agent having a viscosity at25° C. of higher than 500 cP is used, a value at an increasedtemperature where the viscosity is not higher than 500 cP is employed.10. The production method according to claim 8, wherein the granulatingagent has a viscosity of 1 cP or more during the granulation step. 11.The production method according to claim 8, wherein the granulatingagent has a viscosity at 25° C. of 1 cP to 100,000 cP.
 12. Theproduction method according to claim 8, wherein the raw carbon materialcomprises at least one selected from the group consisting of flake,crystalline, and vein natural graphites.
 13. The production methodaccording to claim 8, wherein the raw carbon material has a d₀₀₂ of 0.34nm or less.
 14. The production method according to claim 8, wherein thegranulation step comprises granulating the raw carbon material in thepresence of at least one selected from the group consisting of metalscapable of forming alloys with Li, oxides thereof, amorphous carbon, andgreen coke.
 15. The production method according to claim 8, wherein thegranulation step is carried out in an atmosphere at 0° C. to 250° C. 16.The production method according to claim 8, wherein the granulation stepcomprises placing the graphite in an apparatus comprising a rotatablemember that rotates at a high speed in a casing and having a rotorequipped with a plurality of blades in the casing, and applying any oneof impact, compression, friction, and shear force to the graphite placedin the apparatus by rotating the rotor at a high speed.
 17. Theproduction method according to claim 8, further comprising the step ofdepositing a carbonaceous material having lower crystallinity than theraw carbon material on the granulated carbon material obtained in thegranulation step.